Use TypeAlias where possible for type aliases (#7630)

stdlib/tempfile.pyi

@@ -3,7 +3,7 @@ import sys
 from _typeshed import Self
 from types import TracebackType
 from typing import IO, Any, AnyStr, Generic, Iterable, Iterator, overload
-from typing_extensions import Literal
+from typing_extensions import Literal, TypeAlias
 
 if sys.version_info >= (3, 9):
     from types import GenericAlias
@@ -29,7 +29,7 @@ TMP_MAX: int
 tempdir: str | None
 template: str
 
-_DirT = AnyStr | os.PathLike[AnyStr]
+_DirT: TypeAlias = AnyStr | os.PathLike[AnyStr]
 
 if sys.version_info >= (3, 8):
     @overload