Add mention of protected branches/rulesets WRT the Update branch button (#56239)

Co-authored-by: mc <42146119+mchammer01@users.noreply.github.com>

Author: chiph

content/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/keeping-your-pull-request-in-sync-with-the-base-branch.md

@@ -21,7 +21,9 @@ You can update a pull request's head branch from the command line or the pull re
 * The pull request branch is not up to date with the base branch.
 * The base branch requires branches to be up to date before merging or the setting to always suggest updating branches is enabled.
 
-For more information, see [AUTOTITLE](/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches) and [AUTOTITLE](/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-suggestions-to-update-pull-request-branches).
+> [!NOTE] You may not be able to update using the `Update branch` button if the HEAD branch of your pull request is a protected branch.
+
+For more information, see [AUTOTITLE](/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches), [AUTOTITLE](/repositories/configuring-branches-and-merges-in-your-repository/managing-rulesets/about-rulesets) and [AUTOTITLE](/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-suggestions-to-update-pull-request-branches).
 
 If there are changes to the base branch that cause merge conflicts in your pull request branch, you will not be able to update the branch until all conflicts are resolved. For more information, see [AUTOTITLE](/pull-requests/collaborating-with-pull-requests/addressing-merge-conflicts/about-merge-conflicts).