add scala 2.13.15

[drewfeelsblue]

Fixes #876.

[saeltz]

Thanks for contributing!

Would you please also change the .github/workflows/pr-checks.yml? See https://github.com/scapegoat-scala/scapegoat/pull/869/files for inspiration.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.45%. Comparing base (fa90063) to head (bb062f2).
Report is 38 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #877      +/-   ##
==========================================
- Coverage   88.08%   82.45%   -5.64%     
==========================================
  Files         142       19     -123     
  Lines        1578      302    -1276     
  Branches      278       32     -246     
==========================================
- Hits         1390      249    -1141     
+ Misses        188       53     -135     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[saeltz]

Thanks, @drewfeelsblue!

@mccartney, would you issue a new release please?