Use TypeAlias where possible for type aliases (#7630)

stdlib/re.pyi

@@ -3,6 +3,7 @@ import sre_compile
 import sys
 from sre_constants import error as error
 from typing import Any, AnyStr, Callable, Iterator, overload
+from typing_extensions import TypeAlias
 
 # ----- re variables and constants -----
 if sys.version_info >= (3, 7):
@@ -147,7 +148,7 @@ T = RegexFlag.T
 TEMPLATE = RegexFlag.TEMPLATE
 if sys.version_info >= (3, 11):
     NOFLAG = RegexFlag.NOFLAG
-_FlagsType = int | RegexFlag
+_FlagsType: TypeAlias = int | RegexFlag
 
 if sys.version_info < (3, 7):
     # undocumented