Modernise CI-advanced workflow

[stertooy]

The current CI-advanced workflow is quite outdated:

• Uses old action versions
• Still builds the documentation, even though that was split off into its own workflow

In particular, some of the things this workflow was meant to showcase, such as installing additional system dependencies, are now incorporated into the various gap-actions and corresonding entries in PackageInfo.g.

After updating this workflow, the only remaining difference with the standard CI was the installation of the development version of nq... So I adapted this workflow to also demonstrate running on macOS and Windows.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.06%. Comparing base (bd6d621) to head (3b6bead).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
- Coverage   62.09%   62.06%   -0.03%     
==========================================
  Files           3        4       +1     
  Lines         153      203      +50     
==========================================
+ Hits           95      126      +31     
- Misses         58       77      +19     

see 1 file with indirect coverage changes

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[olexandr-konovalov]

Thanks @stertooy! Of course, this should be updated, the idea behind the package is that one can reuse it, so it should be the latest state of the art setup.

[fingolfin]

Unfortunately this now has a conflict because I merged your other PR first

[stertooy]

Should be resolved now :)

[wilfwilson]

It says that there are still/again conflicts, unfortunately

[stertooy]

Huh? That's weird, for me it's displaying

No conflicts with base branch
Changes can be cleanly merged.

[wilfwilson]

That is so weird!...

I'll try to work out what's happening and sort it out. Thanks for your changes!

[olexandr-konovalov]

I see the same as Wilf. It can be merged, or squashed and merged, but it can't be rebased.

[stertooy]

Right... no idea why I couldn't see this on GitHub itself, but locally I could see the rebase conflicts. Hopefully it's resolved this time.

[olexandr-konovalov]

Now it looks good and ready for the review (@fingolfin @wilfwilson).

[olexandr-konovalov]

LGTM but to be sure I'd like @fingolfin or @wilfwilson who may be better aware of the most recent features.