fix: fix typing for PermissionOverwrite.update

Author: JL710

discord/permissions.py

@@ -860,7 +860,7 @@ def is_empty(self) -> bool:
         """
         return len(self._values) == 0
 
-    def update(self, **kwargs: bool) -> None:
+    def update(self, **kwargs: bool | None) -> None:
         r"""Bulk updates this permission overwrite object.
 
         Allows you to set multiple attributes by using keyword