Add workflow stubtests for macos (#5384)

* Add macos to stubtest

* Add general darwin stubtest exception file

* Adding exceptions and platform ifs

stdlib/selectors.pyi

@@ -41,6 +41,8 @@ if sys.platform != "win32":
         def unregister(self, fileobj: FileDescriptorLike) -> SelectorKey: ...
         def select(self, timeout: Optional[float] = ...) -> List[Tuple[SelectorKey, _EventMask]]: ...
         def get_map(self) -> Mapping[FileDescriptorLike, SelectorKey]: ...
+
+if sys.platform == "linux":
     class EpollSelector(BaseSelector):
         def fileno(self) -> int: ...
         def register(self, fileobj: FileDescriptorLike, events: _EventMask, data: Any = ...) -> SelectorKey: ...