CompatHelper: bump compat for PrettyTables to 3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the PrettyTables package from 1, 2 to 1, 2, 3.
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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.35%. Comparing base (a26ea2e) to head (5a04daf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #422   +/-   ##
=======================================
  Coverage   92.35%   92.35%           
=======================================
  Files          33       33           
  Lines        1804     1804           
=======================================
  Hits         1666     1666           
  Misses        138      138           

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