Changes

testenv: make it pass 'ruff check' linter

I've added 'ruff check' to my pre-commit script. Make it pass initially,
so it can detect future bugs. The missing f-string is a bug that causes
ggsn testsuites with a custom kernel path to not work.

Change-Id: I3e5cd05ce0aa241509d77391c5ed64e618f385ba