Enforce doker build test (#8271)

This PR enforce docker-build test so that every PR will check to make
sure the docker build (which reliesd on if base image, binary, etc
are still correct), is actually available and working.

Note previously, we only check a dry run of docker push, but not actually
build the docker image (as binary was fetched from release version on github).
This PR fetch local binary build instead as there maynot be the same in different
release versions of binary.

This is related 8228

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

.github/workflows/go.test.yml

@@ -121,3 +121,13 @@ jobs:
 
       - name: Test Makefile.docker release/github-push (dry-run)
         run: make VERSION=x DOCKER=x -n release docker-push -f Makefile.docker
+
+      - name: Prepare Docker build
+        run: |
+          for arch in amd64 arm arm64 mips64le ppc64le s390x riscv64 loong64; do
+            mkdir -p build/docker/$arch
+            cp build/linux/$arch/coredns build/docker/$arch/
+          done
+
+      - name: Test Makefile.docker build
+        run: make VERSION=x DOCKER=x -f Makefile.docker docker-build