Add flake8 to remaining muon packages (ATLASRECTS-5740)

Nicolas Koehlerrequested to merge
nkoehler/athena:rec5740 into master

Hi,

this MR adds flake8 checks to the remaining muon packages. It closes https://its.cern.ch/jira/browse/ATLASRECTS-5740.

Best, Nico

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