Fixed LDAP group sync using wrong user filter

LDAP group sync was trying to find users based on the external_auth_id
which is not garunteed to match the username entered so somtimes
the search for a user would fail.

This passes the username to the group sync.
Picked up by @yoyokko in #959.

app/Http/Controllers/Auth/LoginController.php

@@ -103,7 +103,7 @@ class LoginController extends Controller
 
         // Sync LDAP groups if required
         if ($this->ldapService->shouldSyncGroups()) {
-            $this->ldapService->syncGroups($user);
+            $this->ldapService->syncGroups($user, $request->get($this->username()));
         }
 
         $path = session()->pull('url.intended', '/');