ci: run tests + quickstart *nix systems on 4.14.x and 5.0.x

[maxRN]

This PR fixes the pipeline to enable running tests again on Ubuntu and MacOS on OCaml verions 4.14.x and 5.0.x.

Windows builds require some more special attention. There were some errors during compilation of the ssl dependency. Logs can be found here: https://github.com/maxRN/dream/actions/runs/10508356669/job/29112078780

The Mirage tests are also failing, because of some dependency issues which I didn't have time to investigate further. Logs for those can be found here: https://github.com/maxRN/dream/actions/runs/10521553562/job/29152441822 (the other, non-mirage test failures can be ignored - I was just testing something in this run)