Use typing.Self throughout library

discord/webhook/sync.py

@@ -37,7 +37,7 @@ import time
 import re
 
 from urllib.parse import quote as urlquote
-from typing import Any, Dict, List, Literal, Optional, TYPE_CHECKING, Tuple, Type, TypeVar, Union, overload
+from typing import Any, Dict, List, Literal, Optional, TYPE_CHECKING, Tuple, Union, overload
 import weakref
 
 from .. import utils