update workflow to avoid recursive checkout

.github/workflows/docker-build-push-dockerhub.yml

@@ -33,9 +33,12 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v2
-        with:
-          submodules: true
+      - name: checkout
+        uses: actions/checkout@v2
+
+      - name: Git submodule update
+        run: |
+          git submodule update --init
 
       - name: Docker Login
       # You may pin to the exact commit or the version.