use git tag as docker tag

Author: Andrej Sajenko

.github/workflows/gradle.yml

@@ -55,7 +55,7 @@ jobs:
         uses: mr-smithers-excellent/docker-build-push@v4
         with:
           image: asjn83/demo
-          tag: latest
+          tag: ${{ github.ref_name }}
           registry: docker.io
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}