CTest follow-up: migrate CI tests from Azure to GitHub Actions

[EZoni]

We would like to migrate our CI tests from Azure to GitHub Actions, which could lead to better caching thanks to recent ccache improvements by @WeiqunZhang.

Alternatively, we could check if we can make use of more control in Azure Pipelines for caches.

There might be more limitations on parallelism, which we would need to assess once we try the migration.