use LiteralString for sentinel name

type checkers enforce that the first argument to a sentinel is a string literal matching its name, which is enforced by the PEP: see https://peps.python.org/pep-0661/#typing

currently the type checkers contain logic to enforce that the argument is a string literal, but some of this special-casing can be removed if we use `LiteralString` in the stubs

Author: DetachHead

stdlib/builtins.pyi

@@ -2196,7 +2196,7 @@ if sys.version_info >= (3, 15):
     class sentinel:
         __name__: str
         __module__: str
-        def __new__(cls, name: str, /, *, repr: str | None = None) -> sentinel: ...
+        def __new__(cls, name: LiteralString, /, *, repr: str | None = None) -> sentinel: ...
         def __copy__(self, /) -> sentinel: ...
         def __deepcopy__(self, memo: Any, /) -> sentinel: ...
         # `other` can be any legal form for unions.