chore(deps): update boneskull/gh-stack digest to a4ac91c

Author: renovate[bot]

.github/workflows/claude-code-review.yml

@@ -10,5 +10,5 @@ jobs:
     if: |
       github.event.pull_request.head.repo.full_name == github.repository
     # Job body always comes from main so edits to these workflows on a PR cannot break the check.
-    uses: boneskull/gh-stack/.github/workflows/claude-code-review-reusable.yml@1aa24a5ca8eaddc47822b2d799e772255dcf2c6b # main
+    uses: boneskull/gh-stack/.github/workflows/claude-code-review-reusable.yml@a4ac91c022511b771bd278fc3a7460471f6436c2 # main
     secrets: inherit