CI: cancel workflows when PRs are updated

[behlendorf]

Motivation and Context

We want to cancel in-progress workflows for PRs which are updated to ensure the workers are testing useful changes. At the same time we always want to fully test changes which are merged to a branch.

@mcmilk @rincebrain I think this should handle the case mentioned in #16537 (comment).

Description

For checkstyle, zloop, zfs-qemu, and codeql workflows cancel in-progress jobs when the PR is updated.

Directly from GitHub Actions documentation:

The following concurrency group cancels in-progress jobs or run
on pull_request events only; if github.head_ref is undefined, the
concurrency group will fallback to the run ID, which is guaranteed
to be both unique and defined for the run.

https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for-github-actions#example-using-a-fallback-value

How Has This Been Tested?

It hasn't. This is change is solely based on the example in the GitHub documentation.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)