CI does not test install

#̶7̶ ̶c̶o̶u̶l̶d̶ ̶h̶a̶v̶e̶ ̶b̶e̶e̶n̶ ̶d̶e̶t̶e̶c̶t̶e̶d̶ ̶a̶t̶ ̶C̶I̶ ̶t̶i̶m̶e̶

The project build & test could be:
- checkout
- build wheel file
- pip install from wheel file
- run tests

edit: my bad, this is just first startup because the default config doesn't like an uninitialised project. CI improvement is probably still valid though.