Fix merge-bot update command checkout issue

The update command was failing because the checkout action wasn't
specifying which repository to checkout from. This caused it to only
fetch the default branches and not the PR branch.

Added 'repository' parameter to the checkout action to explicitly
specify the head repository, fixing the branch checkout issue.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vilsonrodrigues

.github/workflows/merge-bot.yml

@@ -403,6 +403,7 @@ jobs:
         if: steps.check_perms.outputs.has_permission == 'true'
         uses: actions/checkout@v4
         with:
+          repository: ${{ steps.pr_info.outputs.head_repo }}
           ref: ${{ steps.pr_info.outputs.head_branch }}
           fetch-depth: 0
           token: ${{ secrets.GITHUB_TOKEN }}