Fix cicd

[epierce]

The latest version of Ubuntu does not have a Python 3.6 package, this breaks the CI tests - locking the version to Ubuntu 20 until a 3.6 package is built for Ubuntu 22

How Has This Been Tested?

All tests now run successfully

Types of changes

• [x ] 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 change)

Checklist:

• [x ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x ] All new and existing tests passed.