From 9.1.1 update to 9.5.5，export error。

Configuring gitlab::database
Configuring gitlab::redis
Configuring gitlab::secrets...
Configuring gitlab::sidekiq...
Configuring gitlab::gitaly...
Configuring gitlab::monitoring...
Configuring gitlab::gitlab-workhorse...
Configuring gitlab::unicorn...
Configuring gitlab::timezone...
Configuring gitlab::rack_attack...
Configuring gitlab::ci...
Configuring gitlab::artifacts...
Configuring gitlab::lfs...
Configuring gitlab::mattermost...
Configuring gitlab::project_features...
Configuring gitlab::smtp_settings...
Configuring gitlab::oauth...
Configuring gitlab::ldap...
Configuring gitlab::cron_jobs...
Configuring gitlab::backups...
Configuring gitlab::backups::schedule...
Configuring gitlab::registry...
Configuring gitlab::pages...
Configuring gitlab-shell...
Configuring nginx...
Configuring nginx::gitlab...
Migrating database...
Missing Rails.application.secrets.jws_private_key for production environment. The secret will be generated and stored in config/secrets.yml.

• [[ mysql2 == mysql2 ]]
• exec_as_git bundle exec rake add_limits_mysql
  ++ whoami
  rake aborted!
  ActiveRecord::ActiveRecordError: No such column: merge_request_diffs.st_commits
  /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract_adapter.rb:501:in column_for' /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:791:in change_column_sql'
  /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:531:in change_column' /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/migration.rb:665:in block in method_missing'
  /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/migration.rb:634:in block in say_with_time' /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/migration.rb:634:in say_with_time'
  /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.8/lib/active_record/migration.rb:654:in method_missing' /home/git/gitlab/db/migrate/limits_to_mysql.rb:6:in up'
  /home/git/gitlab/lib/tasks/migrate/add_limits_mysql.rake:8:in block in <top (required)>' /home/git/gitlab/vendor/bundle/ruby/2.3.0/gems/rake-12.0.0/exe/rake:27:in <top (required)>'
  Tasks: TOP => add_limits_mysql
  (See full trace by running task with --trace)

Start with db/migrate/limits_to_mysql.rb and lib/tasks/migrate/add_limits_mysql.rake, then reproduce the add_limits_mysql task using the reported upgrade path. Trace why the migration expects merge_request_diffs.st_commits and verify the upgrade completes without the reported ActiveRecord error.