Try docker instead of docker-container

docker-container does not see local images and always fetches from
remote

.github/workflows/build-ruby.yml

@@ -162,7 +162,7 @@ jobs:
       # Using docker-container engine enables advanced buildx features
       - name: Set up Docker container engine
         run: |
-          docker buildx create --name=container --driver=docker-container --use --bootstrap
+          docker buildx create --name=container --driver=docker --use --bootstrap
 
       # First, build image for x86_64 as it will fail fast
       #
@@ -195,7 +195,7 @@ jobs:
       - name: Build single-arch compiler image (x86_64)
         if: ${{ contains(matrix.arch, 'x86_64') && matrix.libc == 'musl' }}
         run: |
-          docker image list
+          docker image list # image not in builder=container!
           docker buildx build ${{ steps.vars.outputs.SRC }} --builder=container --cache-from=type=registry,ref=${{ steps.vars.outputs.IMAGE }}:${{ steps.vars.outputs.RELEASE_TAG }}-gcc --output=type=image,push=false --platform linux/x86_64 -f ${{ steps.vars.outputs.DOCKERFILE }}.gcc
       # TODO: add CI tag and test