Only run CI checks on relevant changes

[jbcoe]

Fixes #543

[jbcoe]

We need a nice way of running checks defined by a .yml file if the .yml file is edited.

I've tried explicitly adding the relative path of the file that defines a check to the check but it does not seem to work. @Twon any input would be gratefully received.

Update: Fixed it - missing quotes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.60%. Comparing base (be7823e) to head (72b6081).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #544   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files          11       11           
  Lines         750      750           
  Branches       76       76           
=======================================
  Hits          747      747           
  Misses          3        3           

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[Twon]

Looks sensible