CI Break: `tj-actions/changed-files` GitHub Action has been deleted

[lornest]

As per this Hacker News thread, the action tj-actions/changed-files has been removed due to a compromise, causing CI to fail for anyone still using the pipeline provided by this repo.

Currently looking into alternate options for my repo generated from this, if I come up with someone I'll PR here.

[jbw976]

Thanks for sharing this information @lornest. At the least, we should update this template (and all other repos) to point to a immutable digest instead of a mutable tag.

More details about our findings can be seen in crossplane/crossplane#6339