Fix mypy heisenfailure on Windows

Author: oschwald

tests/reader_test.py

@@ -543,6 +543,7 @@ def lookup(pipe) -> None:
                 except:
                     pipe.send(0)
                 finally:
+                    # type: ignore[attr-defined]
                     if worker_class is self.mp.Process:
                         reader.close()
                     pipe.close()