Get CI working with just PIP installs

[shimwell]

To keep the CI concise we can make use of the openmc docker image that includes dagmc.

The trouble is that this docker image currently uses an older version of python and we need minimum python 3.10

If this PR gets merged in then we get python 3.10 in the docker image :tada: and I can continue on the CI that just uses pip installs (no conda)