gha: Set latest tag for default branch.

Author: intersectRaven

.github/workflows/docker-publish.yml

@@ -68,6 +68,8 @@ jobs:
         uses: docker/metadata-action@96383f45573cb7f253c731d3b3ab81c87ef81934 # v5.0.0
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=raw,value=latest,enable={{is_default_branch}}
 
       # Build and push Docker image with Buildx (don't push on PR)
       # https://github.com/docker/build-push-action