Bump GH Actions versions for checkout, pnpm, & node, and use node 20

Also
- clean up and utilize the matrix `node-version`
- Use node caching for pnpm dependencies, as is shown in
  https://github.com/pnpm/action-setup/blob/ac5bf11548bf5e19b8aadb8182072616590fa4a6/README.md#use-cache-to-reduce-installation-time
- Rely on the `packageManager` in package.json for the pnpm version, as
  required by the newer pnpm setup action
  (https://github.com/pnpm/action-setup/blob/ac5bf11548bf5e19b8aadb8182072616590fa4a6/README.md#install-only-pnpm-with-packagemanager)

.github/workflows/build-test.yml

@@ -13,16 +13,20 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [18]
+        node-version: [20]
 
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
-      - name: Setup pnpm
-        uses: pnpm/action-setup@v2
+      - name: Install Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
         with:
-          version: 9
+          node-version: ${{ matrix.node-version }}
+          cache: "pnpm"
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
 
       - run: pnpm install
 

.github/workflows/release.yml

@@ -14,27 +14,22 @@ jobs:
     permissions:
       contents: read
       id-token: write # Needed for https://docs.npmjs.com/generating-provenance-statements
-    strategy:
-      matrix:
-        node-version: [18]
 
     needs: [build-test] # Require standard CI steps to pass before publishing
 
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       # Set up .npmrc file to publish to npm. This also allows NODE_AUTH_TOKEN
       # to work below.
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
         with:
-          node-version: "18.x"
+          node-version: "20.x"
           registry-url: "https://registry.npmjs.org"
 
-      - name: Setup pnpm
-        uses: pnpm/action-setup@v2
-        with:
-          version: 9
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
 
       - run: pnpm install