[CI] PR-label-gating workflow: Exclude `blog` PRs from automatic `ready-to-be-merged` gating

[vitorvasc]

Could somebody with the necessary permissions remove the ready-to-be-merged label? Ideally we're aiming for around March 23rd on this one. Thanks!

I'll create a follow-up issue so the labels workflow handles PRs containing blog posts better. In the meantime, updates and new commits on this PR might re-add the ready-to-be-merged label.

Originally posted by @vitorvasc in #9293 (comment)

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For PRs with the blog label, we could either:

1. Skip the ready-to-be-merged label entirely.
2. Update the current workflow to run once a day and add the ready-to-be-merged label only when the PR is fully approved and the current date matches the publication date.

/cc @open-telemetry/docs-approvers WDYT?

[tiffany76]

Great idea, @vitorvasc. I think option 2 is the more future-proof solution, given my recent limited availability. If it's just me handling blog publishing, I can keep track of when PRs should be merged, so option 1 would be fine. But option 2 opens the workflow so all the Comms maintainers can help with coverage.

I vote for 2️⃣ .

EDIT: Of course, there is still the possibility that the date on the post doesn't get updated, but it is approved, so the label appears. We'll have to be vigilant about scheduling blog posts on our tracker and setting the PR dates accordingly.