Make check-packs action work

[ben-githubs]

Background

There are some issues with the check-packs action, including:

• it always returns successful, even when there are actually issues with packs
• it always adds a "😱 looks like some things could be wrong with the packs!" comment, even when there are no things wrong with the packs
• it never deletes the above comment, even when the problem is resolved

This PR fixes this, so that the comment is only present when pack issues exist, and the action will fail if there are issues with the packs. This will allow us to catch pack issues in the PR phase, as God intended, and not after the fact.

Changes

• update the GHA comment dependency to v3 so that it actually works
• separate the "get check-packs output" and "get check-packs exit code" logic into 2 separate steps, to allow accurate job status reporting

Testing

• Look at all my test commits. I have made sure it works by live testing in Github. I have seen the beginning and the end and I am left but a husk of a man for it.

[ben-githubs]

@arielkr256 this one's good to go!