Improve CI performance

I mainly migrated the CI pipeline to remove deprecated constructs and activate dependency scanning which became available for the Kotlin Gradle DSL recently. I also played around with some new features to skip stage boundaries and run some jobs in parallel. On average this saves us about 5 minutes for a run. The vast majority of the time is still used by the tests. It might be possible to carve out a couple of minutes more but to gain an advantage we would need to split the test runs or find a way to make them faster. The amount of work is not reasonable currently.

I am not sure how to review this, as a lot changed in the file but close to nothing changed in the behavior. I would be OK to use the working pipeline as "proof".