fixes for FormMixin's get_form/get_form_class

django-stubs/core/files/storage.pyi

@@ -1,15 +1,12 @@
 from datetime import datetime
-from io import StringIO, TextIOWrapper
-from typing import Any, List, Optional, Tuple, Union
+from typing import Any, IO, List, Optional, Tuple
 
 from django.core.files.base import File
 from django.utils.functional import LazyObject
 
 class Storage:
     def open(self, name: str, mode: str = ...) -> File: ...
-    def save(
-        self, name: Optional[str], content: Union[StringIO, TextIOWrapper, File], max_length: Optional[int] = ...
-    ) -> str: ...
+    def save(self, name: Optional[str], content: IO[Any], max_length: Optional[int] = ...) -> str: ...
     def get_valid_name(self, name: str) -> str: ...
     def get_available_name(self, name: str, max_length: Optional[int] = ...) -> str: ...
     def generate_filename(self, filename: str) -> str: ...