Use `.format` instead of `%` formatting for strings

[jakobj]

Old style formatting using the % syntax should be replace with new style formatting via .format, see e.g., https://pyformat.info/

[otizonaizit]

Well, now we should move directly to f-strings:

• https://www.python.org/dev/peps/pep-0498/
• https://realpython.com/python-f-strings/
• https://docs.python.org/3/reference/lexical_analysis.html#f-strings