Update Member.php

The public function isLockedOut() in Member.php call LoginAttempt::getByEmail but serves to it the unique_identifier_field.

This PR could allow to extensions to patch the use of uniqueidentifierfield (otherwise it would be necessary to extends the Member Class to override the isLockedOut function, with a lot of problems)

src/Security/Member.php

@@ -382,8 +382,7 @@ class Member extends DataObject
             return false;
         }
 
-        $idField = static::config()->get('unique_identifier_field');
-        $attempts = LoginAttempt::getByEmail($this->{$idField})
+        $attempts = LoginAttempt::getByEmail($this->Email)
             ->sort('Created', 'DESC')
             ->limit($maxAttempts);