tweaks install helpers to remove possible success file before starting ST
redirects ST console output to Github Actions in case of run-tests not detecting any test output. It was required to find #234.
teaches UnitTesting to directly create coverage.xml instead of setting up and running a dedicated task for conversion. This was required as coverage dataformat changed between v4.5 and 7.x. It's a sqlite database now.
Skips coverage on python 3.8 on MacOS, because of #234.
This PR...
success
file before starting ST