Use predictable VMs for jobs in the CI

[ssbarnea]

In general is better not to use -latest runners because they are very often outdated versions, causing problems. As github does not update the name of the runners very often, it is easier to use specific ones. This also prevents surprises when github is changing the runner versions as they do this gradually and -latest ones might point to different runners in different jobs.

Reference: https://github.com/actions/runner-images