fix image tag when pushing a git tag

Author: PhilWun

.github/workflows/dockerhub.yml

@@ -24,6 +24,8 @@ jobs:
           tags: |
             # set latest tag for master branch
             type=raw,value=latest,enable=${{ github.ref == format('refs/heads/{0}', 'master') }}
+            # set tag when pushing a tag
+            type=ref,event=tag
       - name: Login to DockerHub
         uses: docker/login-action@v1
         with: