CompatHelper: bump compat for Compat to 4, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Compat package from 2.2, 3 to 2.2, 3, 4.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

Merging #30 (64ec073) into master (ef5ec84) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #30   +/-   ##
=======================================
  Coverage   98.50%   98.50%           
=======================================
  Files           1        1           
  Lines          67       67           
=======================================
  Hits           66       66           
  Misses          1        1           

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[willtebbutt]

This is redundant now that #34 has been merged