ci: mirror buildkit image to ghcr

.github/workflows/ghcr.yml

@@ -48,10 +48,21 @@ jobs:
 
       - name: Mirror DockerHub
         run: |
-          # DockerHub image we want to mirror
-          image="ubuntu:22.04"
+          # List of DockerHub images to mirror to ghcr.io
+          images=(
+            # Mirrored because used by the mingw-check-tidy, which doesn't cache Docker images
+            "ubuntu:22.04"
+            # Mirrored because used by all linux CI jobs, including mingw-check-tidy
+            "moby/buildkit:buildx-stable-1"
+          )
 
-          # Mirror image from DockerHub to ghcr.io
-          ./crane copy \
-            docker.io/${image} \
-            ghcr.io/${{ github.repository_owner }}/${image}
+          # Mirror each image from DockerHub to ghcr.io
+          for img in "${images[@]}"; do
+            echo "Mirroring ${img}..."
+            # Remove namespace from the image if any.
+            # E.g. "moby/buildkit:buildx-stable-1" becomes "buildkit:buildx-stable-1"
+            dest_image=$(echo "${img}" | cut -d'/' -f2-)
+            ./crane copy \
+              "docker.io/${img}" \
+              "ghcr.io/${{ github.repository_owner }}/${dest_image}"
+          done