Adjust Github Action: Docker Publish

1. Not only publish Docker images when new release tags are created but
   on every push to master, since release frequency is so low.

2. Use newer versions of the various actions (setup-buildx-action,
   login-action, metadata-action, ...) to suppress some deprecation
   warnings see:
   https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

.github/workflows/docker-publish.yml

@@ -2,10 +2,10 @@ name: Docker Publish
 
 on:
   push:
-    tags: [ 'v*.*.*' ]
-
-env:
-  IMAGE_NAME: mjt128/scryer-prolog
+    branches: 
+      - 'master'
+    tags: 
+      - 'v*.*.*'
 
 jobs:
   build:
@@ -18,33 +18,36 @@ jobs:
 
       # Workaround: https://github.com/docker/build-push-action/issues/461
       - name: Setup Docker buildx
-        uses: docker/setup-buildx-action@79abd3f86f79a9d68a23c75a09a9a85889262adf
+        # https://github.com/docker/setup-buildx-action
+        uses: docker/setup-buildx-action@v2.2.1
 
       # Login against Docker registry
-      # https://github.com/docker/login-action
       - name: Log into registry
-        uses: docker/login-action@28218f9b04b4f3f62068d7b6ce6ca5b26e35336c
+        # https://github.com/docker/login-action
+        uses: docker/login-action@v2.1.0
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       # Extract Docker image tag from git tag. E.g. if git tag is "v0.19.1" then use 
-      # Docker image tag "0.19.1". Tag "latest" is automatically synced with newest
-      # version.
-      # https://github.com/docker/metadata-action
+      # Docker image tag "0.19.1". The "latest" tag reflects the most recent build on
+      # master.
       - name: Extract Docker metadata
         id: meta
-        uses: docker/metadata-action@98669ae865ea3cffbcbaa878cf57c20bbf1c6c38
+        # https://github.com/docker/metadata-action
+        uses: docker/metadata-action@v4.1.1
         with:
-          images: docker.io/${{ env.IMAGE_NAME }}
+          images: docker.io/${{ secrets.DOCKERHUB_USERNAME }}/scryer-prolog
           tags: |
             type=semver,pattern={{version}}
+            type=raw,value=latest,enable={{is_default_branch}}
+            # type=raw,value=latest,enable=${{ github.ref == format('refs/heads/{0}', 'master') }}
 
       # Build and push Docker image with Buildx
-      # https://github.com/docker/build-push-action
       - name: Build and push Docker image
         id: build-and-push
-        uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
+        # https://github.com/docker/build-push-action
+        uses: docker/build-push-action@v3.2.0
         with:
           context: .
           push: true