Use TypeAlias where possible for type aliases (#7630)

stubs/urllib3/urllib3/connection.pyi

@@ -1,6 +1,7 @@
 import ssl
 import sys
 from typing import IO, Any, Iterable
+from typing_extensions import TypeAlias
 
 from . import exceptions, util
 from .packages import ssl_match_hostname
@@ -14,7 +15,7 @@ else:
 
     class ConnectionError(Exception): ...
 
-_TYPE_BODY = bytes | IO[Any] | Iterable[bytes] | str
+_TYPE_BODY: TypeAlias = bytes | IO[Any] | Iterable[bytes] | str
 
 class DummyConnection: ...