Feature request: Warnings can be treated as errors

[Joseph-Edwards]

It would be really helpful if there was an option that allowed any warnings to be treated as errors, that then causes workflows to fail. I made a work around in this PR for the digraphs package, and would be happy to make a PR here if this aligns with the goals of the project :)

An alternative solution would involve adding a command line option for GAP itself that enabled this behaviour.