Add running the unittests to the GitHub workflow

[ehogan]

Following #157, running the unittests should be added to the GitHub workflow so that it runs on push for all PRs.

It may be worth configuring pytest so that it can be run from the GitHub workflow and via -O unittest without needing to change directories, see pytest documentation: Configuration: pyproject.toml and pytest documentation: API Reference: testpaths.

Details

• Estimate: small, suitable for solo mission.

[mo-gill]

Have discussed with Emma and pytest not working (despite adding conda pytest url to cmew-env.lock) after adding it to the default.yml workflow as conda environment needs to be reactivated