Many organizations use LDAP in conjunction with other authentication
methods such as SAML or OAuth. If transient LDAP errors cause the
user to become `ldap_blocked` it is desirable to also unblock the
user if the issue resolves itself. Otherwise, the user is unable
to sign-in again without manual intervention or to sign-in once
via LDAP directly. This change enables any sign-in to recheck
LDAP if the user is `ldap_blocked`.

Changelog: added