CI: Test build for all supported client versions.

[mserajnik]

🍰 Pullrequest

This extends the existing test workflow to build for all currently supported client versions (instead of just 1.12.1) with each compiler (GCC, Clang, MSVC) which will help to prevent compilation errors that affect specific client version builds such as this one.

It also makes it so that all available threads are used instead of the previously hardcoded 2.

Proof

• None

Issues

• None

How2Test

• None

Todo / Checklist

• None

[ratkosrb]

Won't this overload the CI cause it's too many builds?

[mserajnik]

20 jobs can run at the same time. Since there are 21 here now, plus the jobs from the other workflows, some won’t start immediately, but only after others have finished.

So, yes, this will increase the overall time each set of workflow runs takes; imo that tradeoff would be worth it, considering there usually aren’t that many PRs/commits at once that would exhaust the available CI resources.