[4.x] Remove Typo inside UserProvider (#9459)

src/Auth/UserProvider.php

@@ -21,7 +21,7 @@ public function retrieveById($identifier)
     }
 
     /**
-     * Retrieve a user by by their unique identifier and "remember me" token.
+     * Retrieve a user by their unique identifier and "remember me" token.
      *
      * @param  mixed  $identifier
      * @param  string  $token