Restrict renaming protected branches to admins

Now, only admins can rename branches that are protected by branch protection rules.

GitHub allows repository collaborators to rename every branch in a repository, with the exception of the default branch.
When a collaborator renames a branch, any non-wildcard branch protection rules that apply to that branch are also changed to match the branch's new name.
Because only admins can modify branch protection rules, renaming of a protected branch is now limited to admin users.

For more information, visit Renaming a branch and Managing a branch protection rule.