Use object values for build matrix

This allows us to avoid the bad switch reimplementation for the
`build.runs-on` value.

Author: simu

.github/workflows/container-image.yml

@@ -62,8 +62,10 @@ jobs:
       fail-fast: false # NOTE(sg): allow matrix jobs to complete even if one of them fails
       matrix:
         platform:
-          - linux/amd64
-          - linux/arm64
+          - name: linux/amd64
+            runner: ubuntu-24.04
+          - name: linux/arm64
+            runner: ubuntu-24.04-arm
     permissions:
       # The permissions are set to allow the job to write to the GitHub Container Registry (GHCR) and read from the repository.
       attestations: write
@@ -80,11 +82,11 @@ jobs:
       repository-projects: read
       security-events: read
       statuses: read
-    runs-on: ${{ matrix.platform == 'linux/amd64' && 'ubuntu-24.04' || matrix.platform == 'linux/arm64' && 'ubuntu-24.04-arm' }}
+    runs-on: ${{ matrix.platform.runner }}
     steps:
     - name: Prepare environment for current platform
       run: |
-        platform=${{ matrix.platform }}
+        platform=${{ matrix.platform.name }}
         echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
     - name: checkout
       uses: actions/checkout@v6
@@ -109,20 +111,20 @@ jobs:
       uses: docker/setup-buildx-action@v4
       with:
         endpoint: builders
-        platforms: ${{ matrix.platform }}
+        platforms: ${{ matrix.platform.name }}
     - name: Build and push by digest
       id: build
       uses: docker/build-push-action@v7
       env:
         DOCKER_BUILDKIT: 1
       with:
         context: .
-        platforms: ${{ matrix.platform }}
+        platforms: ${{ matrix.platform.name }}
         labels: ${{ steps.meta.outputs.labels }}
         annotations: ${{ steps.meta.outputs.annotations }}
         outputs: type=image,name=${{ env.GHCR_IMAGE }},push-by-digest=true,name-canonical=true,push=true,oci-mediatypes=true
-        cache-from: type=gha,scope=${{ github.repository }}-${{ github.ref_name }}-${{ matrix.platform }}
-        cache-to: type=gha,mode=max,scope=${{ github.repository }}-${{ github.ref_name }}-${{ matrix.platform }}
+        cache-from: type=gha,scope=${{ github.repository }}-${{ github.ref_name }}-${{ matrix.platform.name }}
+        cache-to: type=gha,mode=max,scope=${{ github.repository }}-${{ github.ref_name }}-${{ matrix.platform.name }}
         build-args: |
           GITVERSION=${{ needs.get-version.outputs.gitversion }}
           PYVERSION=${{ needs.get-version.outputs.pyversion }}