superuser: Fix typo (PROJQUAY-3924)

[HammerMeetNail]

• Fixes issue with new LDAP_SUPERUSER_FILTER feature

<pre>Running init script &apos;/quay-registry/conf/init/nginx_conf_create.sh&apos;
Running init script &apos;/quay-registry/conf/init/runmigration.sh&apos;
Traceback (most recent call last):
  File &quot;/quay-registry/conf/init/data_migration.py&quot;, line 3, in &lt;module&gt;
    from app import app
  File &quot;/quay-registry/app.py&quot;, line 262, in &lt;module&gt;
    superusers = SuperUserManager(app, authentication)
  File &quot;/quay-registry/data/users/__init__.py&quot;, line 342, in __init__
    self.state = self.init_app(app, authentication)
  File &quot;/quay-registry/data/users/__init__.py&quot;, line 347, in init_app
    manager = FederetedSuperUserManager(app, authentication)
NameError: name &apos;FederetedSuperUserManager&apos; is not defined
</pre>

[Sunandadadi]

lgtm