Tidy up build-multiarch workflow a little.

Just a bunch of small things:

- Remove deleted branch from triggers.
- Pick a start minute at random that's not too close to the hour (just
  to be nice and not bunch up with other people's jobs).
- Move the build matrix config file out of the hidden .github directory,
  so nobody else has to waste time looking for it.
- Just specify ubuntu-latest. We'd rather the build breaks because
  something needs updating to work with the latest supported OS (likely
  easy to fix) rather than it breaks because it got left on a pinned
  version until it went out of support (likely more effort to fix).
- Remove `name` fields where they don't add anything beyond what's
  already in the `id` field.
- Remove `id` fields where they're unused _and_ don't add any info
  beyond what's in the `uses` field.
- Turn off logspew on `checkout` actions. (It's annoying this isn't the
  default, but hey.)
- Clean up some spurious whitespace.

.github/workflows/build-multiarch.yaml

@@ -16,29 +16,28 @@ on:
   push:
     branches:
       - main
-      - dj-maisy/test_shared_matrix
   schedule:
-    - cron: '0 3 * * *'
+    - cron: '34 3 * * *'
 
 jobs:
   configure_builds:
-    name: Configure Build Settings (from config.json)
-    runs-on: ubuntu-22.04
+    name: Read configuration from build-matrix.json
+    runs-on: ubuntu-latest
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
-      - name: Checkout Repo
-        uses: actions/checkout@v4
-      - name: Set Matrix Data
-        id: set-matrix
-        run: echo "matrix=$(jq -c . < .github/config.json)" >> $GITHUB_OUTPUT
+      - uses: actions/checkout@v4
+        with:
+          show-progress: false
+      - id: set-matrix
+        run: echo "matrix=$(jq -c . < build-matrix.json)" >> $GITHUB_OUTPUT
 
   build_and_push_amd64:
     name: Build ruby_${{ join(matrix.version.rubyver, '.') }} for AMD64 and push to GHCR
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
     needs: configure_builds
     strategy:
-      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix)}}
+      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix) }}
     permissions:
       packages: write
     steps:
@@ -49,21 +48,18 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Checkout from GitHub
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
         with:
           ref: ${{ inputs.gitRef || github.ref }}
-
-      - name: Set up Docker BuildX
-        id: buildx
-        uses: docker/setup-buildx-action@v3
+          show-progress: false
+
+      - uses: docker/setup-buildx-action@v3
 
-      - name: Calculate Image Tags
-        id: calculate-image-tags
+      - id: calculate-image-tags
         run: |
           CREATED_DATE="$(date -u +'%Y-%m-%dT%H:%M:%SZ')"
           echo "createdDate=${CREATED_DATE}" >> $GITHUB_OUTPUT
-          
+
       - name: Generate Base Image Metadata
         uses: docker/metadata-action@v5
         id: base-image-metadata
@@ -108,8 +104,7 @@ jobs:
             type=sha,enable=true,prefix=${{ join(matrix.version.rubyver, '.') }}-,suffix=-amd64,format=short
             type=sha,enable=true,priority=100,format=long,prefix=${{ join(matrix.version.rubyver, '.') }}-,suffix=-amd64
 
-      - name: Build Base Image
-        id: build-base-image
+      - id: build-base-image
         uses: docker/build-push-action@v5
         with:
           file: base.Dockerfile
@@ -124,8 +119,7 @@ jobs:
           tags: ${{ steps.base-image-metadata.outputs.tags }}
           labels: ${{ steps.base-image-metadata.outputs.labels }}
 
-      - name: Build Builder Image
-        id: build-builder-image
+      - id: build-builder-image
         uses: docker/build-push-action@v5
         with:
           file: builder.Dockerfile
@@ -143,10 +137,10 @@ jobs:
 
   build_and_push_arm64:
     name: Build ruby_${{ join(matrix.version.rubyver, '.') }} for ARM64 and push to GHCR
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
     needs: configure_builds
     strategy:
-      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix)}}
+      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix) }}
     permissions:
       packages: write
     steps:
@@ -157,26 +151,23 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Checkout from GitHub
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
         with:
           ref: ${{ inputs.gitRef || github.ref }}
+          show-progress: false
 
-      - name: Set up QEMU (on ARM64 Only)
+      - name: Set up QEMU for ARM64 build
         uses: docker/setup-qemu-action@v3
         with:
           platforms: arm64
-
-      - name: Set up Docker BuildX
-        id: buildx
-        uses: docker/setup-buildx-action@v3
 
-      - name: Calculate Image Tags
-        id: calculate-image-tags
+      - uses: docker/setup-buildx-action@v3
+
+      - id: calculate-image-tags
         run: |
           CREATED_DATE="$(date -u +'%Y-%m-%dT%H:%M:%SZ')"
           echo "createdDate=${CREATED_DATE}" >> $GITHUB_OUTPUT
-          
+
       - name: Generate Base Image Metadata
         uses: docker/metadata-action@v5
         id: base-image-metadata
@@ -221,8 +212,7 @@ jobs:
             type=sha,enable=true,prefix=${{ join(matrix.version.rubyver, '.') }}-,suffix=-arm64,format=short
             type=sha,enable=true,priority=100,prefix=${{ join(matrix.version.rubyver, '.') }}-,suffix=-arm64,format=long
 
-      - name: Build Base Image
-        id: build-base-image
+      - id: build-base-image
         uses: docker/build-push-action@v5
         with:
           file: base.Dockerfile
@@ -237,8 +227,7 @@ jobs:
           tags: ${{ steps.base-image-metadata.outputs.tags }}
           labels: ${{ steps.base-image-metadata.outputs.labels }}
 
-      - name: Build Builder Image
-        id: build-builder-image
+      - id: build-builder-image
         uses: docker/build-push-action@v5
         with:
           file: builder.Dockerfile
@@ -261,9 +250,9 @@ jobs:
       - configure_builds
       - build_and_push_amd64
       - build_and_push_arm64
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
     strategy:
-      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix)}}
+      matrix: ${{ fromJson(needs.configure_builds.outputs.matrix) }}
     permissions:
       packages: write
     steps:
@@ -274,11 +263,11 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Checkout from GitHub
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
         with:
           ref: ${{ inputs.gitRef || github.ref }}
-
+          show-progress: false
+
       - name: Create SHA manifest and push for Ruby Base Images
         run: |
           docker manifest create \
@@ -302,7 +291,7 @@ jobs:
             --amend ghcr.io/${{ github.repository_owner }}/govuk-ruby-base:${{ join(matrix.version.rubyver, '.') }}-${{ github.sha }}-amd64 \
             --amend ghcr.io/${{ github.repository_owner }}/govuk-ruby-base:${{ join(matrix.version.rubyver, '.') }}-${{ github.sha }}-arm64
           docker manifest push ghcr.io/${{ github.repository_owner }}/govuk-ruby-base:${{ join(matrix.version.rubyver, '.') }}
-  
+
       - name: Create Ruby Versioned manifest and push for Ruby Builder Images
         run: |
           docker manifest create \