CompatHelper: bump compat for DimensionalData to 0.26, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the DimensionalData package from 0.24, 0.25 to 0.24, 0.25, 0.26. 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.