Use TypeAlias where possible for type aliases (#7630)

stdlib/tty.pyi

@@ -1,10 +1,11 @@
 import sys
 from typing import IO
+from typing_extensions import TypeAlias
 
 if sys.platform != "win32":
     __all__ = ["setraw", "setcbreak"]
 
-    _FD = int | IO[str]
+    _FD: TypeAlias = int | IO[str]
 
     # XXX: Undocumented integer constants
     IFLAG: int