ci: build amd64 and arm64 image on the correct runner

.gitea/workflows/cd.yaml

@@ -31,9 +31,14 @@ jobs:
 
   build_and_push:
     name: Build and push
+    strategy:
+      matrix:
+        arch: [amd64, arm64]
     needs:
       - test
-    runs-on: ubuntu-latest
+    runs-on:
+      - ubuntu-latest
+      - linux_${{ matrix.arch }}
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -62,9 +67,7 @@ jobs:
         with:
           context: .
           file: ./Dockerfile
-          platforms: |
-            linux/amd64
-            linux/arm64
+          platform: linux/${{ matrix.arch }}
           push: true
           tags: |
             ${{ env.DOCKER_REGISTRY }}/t.behrendt/${{ steps.meta.outputs.REPO_NAME }}:${{ steps.meta.outputs.REPO_VERSION }}