ci(update): fix branch name for @octokit/webhooks-definitions updates

Author: gr2m

.github/workflows/update.yml

@@ -21,7 +21,7 @@ jobs:
         with:
           title: "\U0001F6A7 \U0001F916\U0001F4EF Webhooks changed"
           body: "A new release of [@octokit/webhooks](https://github.com/octokit/webhooks) was just released \U0001F44B\U0001F916\n\nThis pull request updates the TypeScript definitions derived from `@octokit/webhooks`. I can't tell if the changes are fixes, features or breaking, you'll have to figure that out on yourself and adapt the commit messages accordingly to trigger the right release, see [our commit message conventions](https://github.com/octokit/openapi/blob/main/CONTRIBUTING.md#merging-the-pull-request--releasing-a-new-version).\n"
-          branch: "${{ github.ref }}"
+          branch: "update-octokit-webhooks"
           author: Octokit Bot <[email protected]>
           commit-message: "WIP: Webhooks changed - please review"
           labels: "maintenance"