Revert #3402 (check-versions running on forks)

[pepopowitz]

Description

Reverts commit #3402.

Those changes were resulting in inaccurate, noisy comments from the check-versions workflow. Rather than listing the differences between the PR and its target branch at the time the PR was opened, it was listing the differences between the PR and its target branch right now. When the main branch had evolved since opening the PR, that meant the check-versions comment listed basically everything that had been merged since the PR was opened. Reverting this PR will put us back in a place where the check-versions workflow doesn't work for forked PRs, but it is giving accurate messages for 99% of our PRs (which are local instead of forked).

I thought I'd tested this case in #3396, but the workflow seems to be functioning differently than it was in my tests.

I'll reopen #3358 to track the need to fix the check-versions workflow for forked PRs.

When should this change go live?

• This change is not yet live and should not be merged until {ADD_DATE} (apply hold label or convert to draft PR)?
• There is no urgency with this change.
• This change or page is part of a marketing blog, conference talk, or something else on a schedule.
• This functionality is already available but undocumented.
• This is a bug fix or security concern.

PR Checklist

• I have added changes to the relevant /versioned_docs directory, or they are not for an already released version.
• I have added changes to the main /docs directory (aka /next/), or they are not for future versions.
• My changes require an Engineering review, and I've assigned an engineering manager or tech lead as a reviewer, or my changes do not require an Engineering review.
• My changes require a technical writer review, and I've assigned @christinaausley as a reviewer, or my changes do not require a technical writer review.

[akeller]

Thank you. I know this has been a bit of a thorn this week for you, but I appreciate your flexibility here.