COMPAT: update for latest flake8 (#23363)

Author: TomAugspurger

pandas/core/groupby/__init__.py

@@ -1,4 +1,4 @@
-from pandas.core.groupby.groupby import GroupBy  # flake8: noqa
-from pandas.core.groupby.generic import (
-    SeriesGroupBy, DataFrameGroupBy, PanelGroupBy)  # flake8: noqa
-from pandas.core.groupby.grouper import Grouper  # flake8: noqa
+from pandas.core.groupby.groupby import GroupBy  # noqa: F401
+from pandas.core.groupby.generic import (  # noqa: F401
+    SeriesGroupBy, DataFrameGroupBy, PanelGroupBy)
+from pandas.core.groupby.grouper import Grouper  # noqa: F401

pandas/util/testing.py

@@ -762,7 +762,7 @@ def ensure_clean(filename=None, return_filelike=False):
         finally:
             try:
                 os.close(fd)
-            except Exception as e:
+            except Exception:
                 print("Couldn't close file descriptor: {fdesc} (file: {fname})"
                       .format(fdesc=fd, fname=filename))
             try: