Handle deleted config files when running package-and-qa on feature flag config changes

In !68814 (merged) we added the ability to automatically run package-and-qa when a feature flag config YAML file changes in an MR.

That works fine for new files, and changes to existing files, but it doesn't work when files are deleted. That means we won't run package-and-qa in MRs when a feature flag is removed from the codebase, which could be a good thing to do.

Proposal

Automatically run package-and-qa when a feature flag config file is deleted.