Re: [PATCH v4 00/12] ci: replace our Azure Pipeline by GitHub Actions

> Our Azure Pipeline has served us well over the course of the past year or
> so, steadily catching issues before the respective patches hit the next
> branch.
>
> There is a GitHub-native CI system now, though, called "GitHub Actions"
> [https://github.com/features/actions] which is essentially on par with Azure
> Pipelines as far as our needs are concerned, and it brings a couple of
> advantages:
>
>  * It is substantially easier to set up than Azure Pipelines: all you need
>    is to add the YAML-based build definition, push to your fork on GitHub,
>    and that's it.
>  * The syntax is a bit easier to read than Azure Pipelines'.
>  * We get more concurrent jobs (Azure Pipelines is limited to 10 concurrent
>    jobs).
>
> With this change, users also no longer need to open a PR at
> https://github.com/git/git or at https://github.com/gitgitgadget/git just to
> get the benefit of a CI build.
>
> Sample run on top of dd/ci-musl-libc with dd/test-with-busybox merged:
> https://github.com/sgn/git/actions/runs/73179413
>
> Sample run when this series applied into git-for-windows
> https://github.com/git-for-windows/git/runs/568625109
>
> Change from v3:
> - Use build matrix
> - All dependencies are install by scripts
> - stop repeating environment variables
> - build failure's artifacts will be uploaded