* feat: run jobs in parallel
This changes fixes and restructures the parallel execution of jobs.
The previous changes limiting the parallel execution did break this
and allowed only one job in parallel.
While we run #CPU jobs in parallel now, the jobs added per job-matrix
add to this. So we might over-commit to the capacity, but at least
it is limited.
* fix: correctly build job pipeline
The job pipeline should just append all required pipeline steps.
The parallelism will be handled by the ParallelExecutor and we
shouldn't handle it during building the pipelines.
Also this adds a test, that the ParallelExecutor does run
a limited amount of parallel goroutines.
* test: correct test implementation
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
