mgr/volumes: fix various flake8 issues

[Crossbears]

Fixes: https://tracker.ceph.com/issues/51406
Signed-off-by: Jingya Su jingyasu@my.yorku.ca

[varshar16]

Please add title to the commit message and email address should be within angular braces

[github-actions]

This pull request has been automatically marked as stale because it has not had any activity for 60 days. It will be closed if no further activity occurs for another 30 days.
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[github-actions]

This pull request has been automatically closed because there has been no activity for 90 days. Please feel free to reopen this pull request (or open a new one) if the proposed change is still appropriate. Thank you for your contribution!