Make all params positional-only in slice.__new__ (#12900)

positional only __new__

Author: randolf-scholz

stdlib/builtins.pyi

@@ -948,10 +948,10 @@ class slice(Generic[_StartT, _StopT, _StepT]):
     @property
     def stop(self) -> _StopT: ...
     @overload
-    def __new__(cls, stop: int | None) -> slice[int | MaybeNone, int | MaybeNone, int | MaybeNone]: ...
+    def __new__(cls, stop: int | None, /) -> slice[int | MaybeNone, int | MaybeNone, int | MaybeNone]: ...
     @overload
     def __new__(
-        cls, start: int | None, stop: int | None, step: int | None = None
+        cls, start: int | None, stop: int | None, step: int | None = None, /
     ) -> slice[int | MaybeNone, int | MaybeNone, int | MaybeNone]: ...
     @overload
     def __new__(cls, stop: _T2, /) -> slice[Any, _T2, Any]: ...