add unix workflow

[matbesancon]

This will probably break for now. I took the structure from https://github.com/ERGO-Code/HiGHS/blob/master/.github/workflows/build-windows.yml

[fschloesser]

looks good to me so far, i think we could even try to add windows-latest for the os, but then maybe we have to take out the shell, since bash is the default anyways for unix and windows should run on powershell https://dev.to/pwd9000/github-actions-all-the-shells-581h

[matbesancon]

ping @gasse, can you activate / allow workflows for this PR?

[gasse]

Hi @matbesancon , I have no idea how to activate / allow workflows :P Do you want me to merge this pull request? Maybe @AntoinePrv knows better what to do?

[matbesancon]

it might require allowing actions to run, either in this PR if there is the option, or at the repo level yes

[AntoinePrv]

It seems to be enabled, but I don't see the message to allow running workflow for first time contributors...
IIRC Github Actions do not run the first time, I'll commit an empty workflow to the main branch.

[AntoinePrv]

The workflow is not valid. .github/workflows/ci.yml (Line: 15, Col: 9): A sequence was not expected

These Yaml configs are really a nightmare to debug...