CompatHelper: bump compat for ModelingToolkit to 9 for package docs, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the ModelingToolkit package from 8 to 8, 9 for package docs.
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 47.47%. Comparing base (156e65b) to head (50711d7).
Report is 2 commits behind head on master.

❗ Current head 50711d7 differs from pull request most recent head 9fad71e. Consider uploading reports for the commit 9fad71e to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #383       +/-   ##
===========================================
- Coverage   87.44%   47.47%   -39.98%     
===========================================
  Files          46       46               
  Lines        2741     2717       -24     
===========================================
- Hits         2397     1290     -1107     
- Misses        344     1427     +1083     

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