Use f-strings

Should just use f-strings where applicable instead of concatenating.
Will improve readability and performance and handles different types better (i.e. not always necessary to cast to strings).

Start by searching the Python source for string concatenation and review each occurrence to determine which cases are applicable. The work is complete when applicable concatenations use f-strings without changing the bot's behavior; no specific files or tests are named in the issue.

Written by the indexing model from the issue text.