Fix IMAGE_REPO to include ghcr.io registry prefix for forks

The metadata step was only setting image_repo to the repository owner
(e.g., 'chaptersix') instead of the full registry path ('ghcr.io/chaptersix').
This caused Docker to try pushing to Docker Hub instead of GHCR.

Author: chaptersix

.github/workflows/build-and-publish.yml

@@ -112,7 +112,7 @@ jobs:
           if [[ "$REPO_OWNER" == "temporalio" ]]; then
             echo "image_repo=temporalio" >> $GITHUB_OUTPUT
           else
-            echo "image_repo=$REPO_OWNER" >> $GITHUB_OUTPUT
+            echo "image_repo=ghcr.io/$REPO_OWNER" >> $GITHUB_OUTPUT
           fi
 
       - name: Check if release is latest