[psutil] add overloads for cpu_affinity (#15112)

Author: mr-c

stubs/psutil/psutil/__init__.pyi

@@ -198,7 +198,10 @@ class Process:
     if sys.platform != "darwin":
         def io_counters(self) -> pio: ...
         def ionice(self, ioclass: int | None = None, value: int | None = None) -> pionice: ...
-        def cpu_affinity(self, cpus: list[int] | None = None) -> list[int] | None: ...
+        @overload
+        def cpu_affinity(self, cpus: None = None) -> list[int]: ...
+        @overload
+        def cpu_affinity(self, cpus: list[int]) -> None: ...
         def memory_maps(self, grouped: bool = True): ...
     if sys.platform == "linux":
         def rlimit(self, resource: int, limits: tuple[int, int] | None = ...) -> tuple[int, int]: ...