Use TypeAlias where possible for type aliases (#7630)

stdlib/_curses.pyi

@@ -1,10 +1,10 @@
 import sys
 from _typeshed import SupportsRead
 from typing import IO, Any, NamedTuple, overload
-from typing_extensions import final
+from typing_extensions import TypeAlias, final
 
 if sys.platform != "win32":
-    _chtype = str | bytes | int
+    _chtype: TypeAlias = str | bytes | int
 
     # ACS codes are only initialized after initscr is called
     ACS_BBSS: int