tweaks to make test pass on Piz Daint

Description

This merge request introduces changes to the test suite, which were required to pass the tests on Piz Daint. In particular, the dipole matrix elements in the original tests were unconverged and changed a lot with changed to the setup.

News snippet

test suite updates to make results a bit better converged.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.