Replace the travis test with Github Actions as we already stopped using travis a while ago.
Also update a few mixed references to the old Python 3.7 dependency (it is now 3.9)
~Draft status: still need to verify the github workflow runs as intended.~
Replace the travis test with Github Actions as we already stopped using travis a while ago. Also update a few mixed references to the old Python 3.7 dependency (it is now 3.9)
~Draft status: still need to verify the github workflow runs as intended.~