stubtest fixes

Author: Viicos

django-stubs/core/files/uploadedfile.pyi

@@ -42,6 +42,7 @@ class InMemoryUploadedFile(UploadedFile):
         charset: str | None,
         content_type_extra: dict[str, str] | None = ...,
     ) -> None: ...
+    def open(self, mode: str | None = ...) -> Self: ...
 
 class SimpleUploadedFile(InMemoryUploadedFile):
     def __init__(self, name: str, content: bytes | None, content_type: str = ...) -> None: ...