Fix updating of branches in mirrored repository

CHANGELOG-EE

 v 8.5.0 (unreleased)
+  - Fix updating of branches in mirrored repository
 
 v 8.4.1
   - No EE-specific changes

app/helpers/application_helper.rb

@@ -142,7 +142,7 @@ module ApplicationHelper
     return false unless project.repository.branch_names.include?(event.branch_name)
 
     # Skip if this was a mirror update
-    return false if project.mirror? && project.up_to_date_with_upstream?(event.branch_name)
+    return false if project.mirror? && project.repository.up_to_date_with_upstream?(event.branch_name)
 
     true
   end

app/services/git_push_service.rb

@@ -59,7 +59,7 @@ class GitPushService
     @push_data = build_push_data(oldrev, newrev, ref)
 
     branch_name = Gitlab::Git.ref_name(ref)
-    mirror_update = project.mirror? && project.up_to_date_with_upstream?(branch_name)
+    mirror_update = project.mirror? && project.repository.up_to_date_with_upstream?(branch_name)
 
     EventCreateService.new.push(project, user, @push_data)
     project.execute_hooks(@push_data.dup, :push_hooks)