Fix linting

[AlistairNorman]

Summary

Rubocop and eslint linting were both erroring. Running Rubocop and migrating to a new kind of config file fixed these issues.

Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.50%. Comparing base (b2b3f2e) to head (99ed261).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6420   +/-   ##
=======================================
  Coverage   89.50%   89.50%           
=======================================
  Files         981      981           
  Lines       20479    20479           
=======================================
  Hits        18330    18330           
  Misses       2149     2149           

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