CompatHelper: bump compat for FixedPointNumbers to 0.9, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the FixedPointNumbers package from 0.8 to 0.8, 0.9.
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 95.91%. Comparing base (b656cf7) to head (bcc38b3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #578      +/-   ##
==========================================
- Coverage   96.75%   95.91%   -0.85%     
==========================================
  Files           9        9              
  Lines        1296     1225      -71     
==========================================
- Hits         1254     1175      -79     
- Misses         42       50       +8     

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