CI/CLN: Add more test file linting
Fixing use of pd.Index when Index is imported directly
lgtm merge on green Thx for fixing the issue introduced through my join fix. CI run probably before you added this check the last time. > Thx for fixing the issue introduced through my join fix. CI run probably before you added this check the last time.

NP, yeah I think it was just merged after the PR last merged master