[ci] Deprecate flake8 (#8409)

* [ci] Deprecate flake8

* Addressing @villebro's comments

superset/examples/energy.py

@@ -25,6 +25,7 @@ from sqlalchemy.sql import column
 from superset import db
 from superset.connectors.sqla.models import SqlMetric
 from superset.utils import core as utils
+
 from .helpers import get_example_data, merge_slice, misc_dash_slices, Slice, TBL