CompatHelper: bump compat for PowerModels to 0.21 for package OptimizationFrameworks, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the PowerModels package from 0.19 to 0.19, 0.21 for package OptimizationFrameworks. 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.