CompatHelper: bump compat for IntervalArithmetic to 0.20, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the IntervalArithmetic package from 0.15, 0.16, 0.17 to 0.15, 0.16, 0.17, 0.20.
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

Base: 98.53% // Head: 98.53% // No change to project coverage 👍

Coverage data is based on head (9a24bc4) compared to base (b85ee86).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #28   +/-   ##
=======================================
  Coverage   98.53%   98.53%           
=======================================
  Files           7        7           
  Lines         273      273           
=======================================
  Hits          269      269           
  Misses          4        4           

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