Switch repository secrets to using f-strings

[s-t-e-v-e-n-k]

New code written before we switched to f-strings need to get updated to
using them, so do so.

[codecov-io]

Codecov Report

Merging #1867 (d49a107) into master (b2232c8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1867   +/-   ##
=======================================
  Coverage   98.87%   98.87%           
=======================================
  Files         108      108           
  Lines       11044    11044           
=======================================
  Hits        10920    10920           
  Misses        124      124           

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