CI: Update checkstyle image to ubuntu-24.04

[behlendorf]

Motivation and Context

Experiment with updating the checkstyle builder to pulling in newer packages. This will likely result in some new shellcheck, libabigail, mandoc, or flake8 warning which will need to be resolved before this can be merged.

Description

With a new release cycle starting now is a good time to update the checkstyle builder to the latest Ubunutu 24.04 LTS.

How Has This Been Tested?

We'll see what new things the CI warns about.

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)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• 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)