Add helpful details to fixture error message

The database fixtures for development can fail when the database is
being re-created without having deleted the old repositories from
Gitaly. This expands the error message to provide a hint about how
to fix that.

ee/db/fixtures/development/32_compliance_dashboard_merge_requests.rb

@@ -66,6 +66,8 @@ class Gitlab::Seeder::ComplianceDashboardMergeRequests
 
       merge_request
     end
+  rescue AccessDeniedError
+    raise AccessDeniedError.new("If you are re-creating your GitLab database, you should also delete your old repositories located at $GDK/repositories/@hashed")
   end
 
   def create_pipeline!(project, ref, commit, status)