PEP 604: Remove some more uses of Union/Optional (#7515)

The following patterns still break mypy:

1. `type[]` at top level fails
2. `tuple[T1, T2]` at top level fails (but `tuple[T1, ...]` is fine)
3. `T1 | Callable[..., T2 | T3]` fails, but only <=3.9

This PR cleans up usage of `Union` and `Optional` outside these patterns.

stubs/requests/requests/sessions.pyi

@@ -1,5 +1,5 @@
 from _typeshed import Self, SupportsItems
-from typing import IO, Any, Callable, Iterable, Mapping, MutableMapping, Optional, Text, TypeVar, Union
+from typing import IO, Any, Callable, Iterable, Mapping, MutableMapping, Text, TypeVar, Union
 
 from urllib3 import _collections
 
@@ -47,7 +47,7 @@ class SessionRedirectMixin:
     def rebuild_proxies(self, prepared_request, proxies): ...
     def should_strip_auth(self, old_url, new_url): ...
 
-_Data = Union[None, Text, bytes, Mapping[str, Any], Mapping[Text, Any], Iterable[tuple[Text, Optional[Text]]], IO[Any]]
+_Data = Text | bytes | Mapping[str, Any] | Mapping[Text, Any] | Iterable[tuple[Text, Text | None]] | IO[Any] | None
 
 _Hook = Callable[[Response], Any]
 _Hooks = MutableMapping[Text, _Hook | list[_Hook]]