fix: pass proper ref to metadata-action (#298)

When not using a custom value, `docker/metadata-action` takes the ref
from `github.ref`. However, the value of that is `refs/heads/main` when
the workflow is triggered by `workflow_run`. That cannot be parsed into
a semver, and the result is no tags in metadata, which then makes the
docker push fail.

The fix is to extract the value from what the `Determine ref` step
determines (which is the one that Releaser inferred from
`version.json`). A match regex is also provided so that both `v1.2.3`
(what we will get when `workflow_run`) and `refs/tags/v1.2.3` (what we
will get when pushing a tag) work.

Author: volmedo

.github/workflows/publish-ghcr.yml

@@ -142,7 +142,7 @@ jobs:
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
           tags: |
-            type=semver,pattern={{version}}
+            type=semver,pattern={{version}},value=${{ steps.ref.outputs.ref }},match=v[0-9].*
 
       - name: Build and push
         uses: docker/build-push-action@v6