Add Python 3.8 setup step to workflows

[BrianJKoopman]

Description

The build image workflow failed on recent merge to develop. This step worked fine in the checks to the PR in question (#158). There was a missing Python environment setup step, which is added here. This should fix things.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Unless I am preparing a release, I have opened this PR onto the develop branch.

[BrianJKoopman]

CI Pipeline fix, sorry for the noise. Merging...