Update gitlab_omniauth-ldap to v2.2.0

This relaxes the dependency of OmniAuth to make it possible to upgrade
to OmniAuth v2: https://gitlab.com/gitlab-org/gitlab/-/issues/30073

No code changes are present:
https://my.diffend.io/gems/gitlab_omniauth-ldap/2.1.1/2.2.0

Changelog: changed