change Change IO/IOBase.__exit__ return type to None (#7471)

stdlib/io.pyi

@@ -72,7 +72,7 @@ class IOBase:
     def __enter__(self: Self) -> Self: ...
     def __exit__(
         self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
-    ) -> bool | None: ...
+    ) -> None: ...
     def close(self) -> None: ...
     def fileno(self) -> int: ...
     def flush(self) -> None: ...