Reporting rebasing need only once

[vmx]

There's a GitHub action that checks if a rebase is needed. It posts a comment every hour.

I'm currently watching this repo and it would be great if there wouldn't be so many events happening if nothing really changes. I propose using something like https://github.com/peter-evans/find-comment to check if the comment already exists and in case it does, skipping to post another one.

[huitseeker]

This would be a great improvement! You'd try searching for a comment containing the current commit hash right before this step:
https://github.com/lurk-lab/neptune/blob/d4638882bc33335166a01b3e83ea79f30e621686/.github/workflows/upstream_update.yml#L88-L94