Splitting up MD testing for faster turnaround

[alexhroom]

For a faster turnaround on pull request tests, we are considering splitting the MD testing into 'fast' tests and more complex tests. The fast tests will run on a PR, with more complex ones as a cron job. Does anyone with more experience into the MD tests have an idea of how well this split may work?

[Anders-Markvardsen]

This is a super suggestion and thanks for implementing it:)

[franzlang]

this has now been implemented as part of the following issues and PRs:
Travis: #671 and #712
GitHub Actions: #749 and #752