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

[github-actions[bot]]

This pull request changes the compat entry for the ModelingToolkit package from 8.49 to 8.49, 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.