[CI] Fixed missing import

gef.py

@@ -82,7 +82,7 @@
 from io import StringIO, TextIOWrapper
 from types import ModuleType
 from typing import (Any, ByteString, Callable, Dict, Generator, Iterable,
-                    Iterator, List, NoReturn, Optional, Sequence, Tuple, Type,
+                    Iterator, List, NoReturn, Optional, Sequence, Set, Tuple, Type,
                     Union)
 from urllib.request import urlopen