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

[github-actions]

This pull request changes the compat entry for the PrettyTables package from 2.1,2.2 to 2.1,2.2, 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.

[github-actions]

ParetoSmooth.jl documentation for PR #114 is available at:
https://TuringLang.github.io/ParetoSmooth.jl/previews/PR114/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.26%. Comparing base (f76b243) to head (a640d42).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #114      +/-   ##
==========================================
+ Coverage   84.00%   84.26%   +0.26%     
==========================================
  Files          11       11              
  Lines         400      375      -25     
==========================================
- Hits          336      316      -20     
+ Misses         64       59       -5     

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