As a maintainer of Spack I want to have a CI workflow that automatically detects which are the pull requests that modify Spack's core so that I can request a more thorough testing only for them.

Rationale

Recently we have experienced slow-downs with our CI when receiving a large number of PRs on the same day. The major bottleneck was the availability of a MacOS worker on Travis CI.

Most of the PRs were just proposing minimal modifications to packages, so for them a MacOS worker was unnecessary. The rationale here is to identify automatically which are the PRs that need more thorough testing and require more resources only for them.

Description

It seems that Github actions might help with this with their filtering capabilities that permit to filter on the paths that have been modified in a PR. We might then shape our workflow depending on the parts that are effectively modified.

Additional information

Related effort is #5842. It's more demanding on contributors since the workflows are static and based on the name of the branch.