This is a follow up to T307209: mwaddlink CI fails with "No module named pip"

In mwaddlink, we currently run pytest twice. We run it in the test variant. Then, because T277777: Support copying files from run containers into the workspace for use in other stages wasn't solved at the time of the pipeline setup, we run it again to generate coverage reports. This is inefficient, and also requires the coverage step to know about python (see T307209), when it really should just run the sonarqube scanner tool to upload relevant files.

I can't figure out the exact syntax for copying the files from test to coverage variant, so help needed here.