CI: Autogenerate a PR comment for contributors making changes to the `cuda_bindings/` directory

[leofang]

Everywhere in this repo is OSS and Apache-2.0 and can accept external contributions, except for the cuda_bindings/ directory.

We should run a preliminary scan (preferably without having to /ok to test, but not as part of pre-commit which does not make sense) and post a comment to the PR if the binding files are touched by external contributors.

This relieves team members from having to reject in part or in full of the contribution.