Use TypeAlias where possible for type aliases (#7630)

stubs/freezegun/freezegun/api.pyi

@@ -2,9 +2,10 @@ from collections.abc import Awaitable, Callable, Iterator, Sequence
 from datetime import date, datetime, timedelta
 from numbers import Real
 from typing import Any, TypeVar, overload
+from typing_extensions import TypeAlias
 
 _T = TypeVar("_T")
-_Freezable = str | datetime | date | timedelta
+_Freezable: TypeAlias = str | datetime | date | timedelta
 
 class TickingDateTimeFactory:
     def __init__(self, time_to_freeze: datetime, start: datetime) -> None: ...