CompatHelper: bump compat for Ipopt to 0.8, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Ipopt package from 0.6, 0.7 to 0.6, 0.7, 0.8.
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-commenter]

Codecov Report

Merging #38 (a08fe50) into master (03615d6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #38   +/-   ##
=======================================
  Coverage   42.89%   42.89%           
=======================================
  Files          21       21           
  Lines        3096     3096           
=======================================
  Hits         1328     1328           
  Misses       1768     1768           

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