CompatHelper: bump compat for DomainSets to 0.7 for package StiffODE, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the DomainSets package from 0.6 to 0.6, 0.7 for package StiffODE. 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.