Use positional-only arguments for IO (#6851)

stdlib/bz2.pyi

@@ -88,7 +88,7 @@ def open(
     newline: str | None = ...,
 ) -> BZ2File | TextIO: ...
 
-class BZ2File(BaseStream, IO[bytes]):  # type: ignore # argument disparities between base classes
+class BZ2File(BaseStream, IO[bytes]):
     def __enter__(self: Self) -> Self: ...
     if sys.version_info >= (3, 9):
         @overload