fix: update Docker build workflow to conditionally set platforms based on branch

- Modified the platforms setting in the Docker build workflow to conditionally include ARM64 support only when on the main branch, enhancing build efficiency and flexibility.

Author: atyrode

.github/workflows/docker-build.yml

@@ -53,7 +53,7 @@ jobs:
         with:
           context: .
           push: ${{ github.event_name != 'pull_request' }}
-          platforms: linux/amd64,linux/arm64
+          platforms: ${{ github.ref == 'refs/heads/main' && 'linux/amd64,linux/arm64' || 'linux/amd64' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha