Run `flynt` over code base to convert old-style Python % formats to f-strings

[mhucka]

What is the task?

There are still some old-style %-formatted strings in some of the Python files. We should run flynt over the code base.

(Optional) Do you have ideas or preferences for the approach?

This should be done in one shot and the merge commit should be added to .git-blame-ignore-revs so that git blame ignores it.

How urgent is this for you?

None