CompatHelper: bump compat for Trixi to 0.9 for package test, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Trixi package from 0.7, 0.8 to 0.7, 0.8, 0.9 for package test.
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.

[ranocha]

Since #41 has already been merged, CI should work. However, it is better to merge several CompatHelper PRs first into a single PR to really check whether CI passes before merging stuff into main.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.78%. Comparing base (20c9ebd) to head (f624b39).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #42   +/-   ##
=======================================
  Coverage   81.78%   81.78%           
=======================================
  Files           8        8           
  Lines         829      829           
=======================================
  Hits          678      678           
  Misses        151      151           

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