STYLE: Update Python string formatting syntax

[Leengit]

Replace the likes of old-style "My file is {file}".format(file=my_file) with new-style f"My file is {my_file}".

[dzenanz]

I forgot this is software guide repo. This needs to be done in main repo too.

[Leengit]

I forgot this is software guide repo. This needs to be done in main repo too.

Submitted as ITK Issue #3239

[jhlegarreta]

PR #179 did not close this since #179 (comment) was not on the PR opening message. Closing now. Thanks for having addressed this Lee.