Add __all__ part 2 (#13719)

---------

Co-authored-by: Avasam <samuel.06@hotmail.com>

stubs/WTForms/@tests/stubtest_allowlist.txt

@@ -1,6 +1,3 @@
-# TODO: missing from stub
-wtforms.form.__all__
-
 # Error: is not present at runtime
 # =============================
 # This is hack to get around Field.__new__ not being able to return

stubs/WTForms/wtforms/form.pyi

@@ -83,3 +83,5 @@ class Form(BaseForm, metaclass=FormMeta):
     def __setitem__(self, name: str, value: None) -> None: ...  # type: ignore[override]
     def __delitem__(self, name: str) -> None: ...
     def __delattr__(self, name: str) -> None: ...
+
+__all__ = ("BaseForm", "Form")