Avoid protected branches checks when verifying access without branch name

GitlabShell verify access sending ‘_any’ as the changes made on the git command, in those cases Gitlab::Checks::ChangeAccess won’t receive a branch_name so we don’t need to check for access to the 
protected branches on that repository. So we avoid some git operations in case the are not cached (empty_repo?) and some database lookups to get protected branches.

These request is happening in every push.

CHANGELOG

@@ -115,6 +115,7 @@ v 8.12.0 (unreleased)
   - Avoid conflict with admin labels when importing GitHub labels
   - User can edit closed MR with deleted fork (Katarzyna Kobierska Ula Budziszewska) !5496
   - Fix repository page ui issues
+  - Avoid protected branches checks when verifying access without branch name
   - Add information about user and manual build start to runner as variables !6201 (Sergey Gnuskov)
   - Fixed invisible scroll controls on build page on iPhone
   - Fix error on raw build trace download for old builds stored in database !4822

lib/gitlab/checks/change_access.rb

@@ -23,6 +23,7 @@ module Gitlab
       protected
 
       def protected_branch_checks
+        return unless @branch_name
         return unless project.protected_branch?(@branch_name)
 
         if forced_push? && user_access.cannot_do_action?(:force_push_code_to_protected_branches)