fix: use full refspec for pushing to rc branch

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Author: zimeg

.github/workflows/release.yml

@@ -97,7 +97,7 @@ jobs:
           git config user.name "slack-cli-releaser[bot]"
           git config user.email "122933866+slack-cli-releaser[bot]@users.noreply.github.com"
           make rc RELEASE_VERSION="$RELEASE_VERSION"
-          git push origin "HEAD:rc" --force
+          git push origin "HEAD:refs/heads/rc" --force
 
       - name: Create or update release PR
         if: steps.version.outputs.has_changes == 'true'