Pin ubuntu-20.04 in workflow files

[solvaholic]

and use github/super-linter:v3

Description

Pin ubuntu-20.04 in workflow files and use github/super-linter:v3

Motivation and Context

fixes #46

How Has This Been Tested?

It hasn't. The affected workflow files run shell scripts and/or actions that are happy to run on -latest, so I anticipate zero impact.

Screenshots (if appropriate):

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] I have read the CONTRIBUTING document.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] All new and existing tests passed.