Update main.yml

Using the current/correct version of the action checkout.

.github/workflows/main.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Ziege - ${{ matrix.target }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Setup Zig
         uses: korandoru/setup-zig@v1
         with: