Rollup merge of rust-lang#144176 - Kobzol:bors-labels-blocking, r=oli-obk

Add approval blocking labels for new bors

If a PR contains these labels, new bors won't let anyone approve it. We don't merge PRs using new bors yet, ofc, but I wanted to prepare this so that I don't forget about it.

This was proposed here: [#t-lang/meetings > Triage meeting 2025-07-23 @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/410673-t-lang.2Fmeetings/topic/Triage.20meeting.202025-07-23/near/529407150) and implemented [here](rust-lang/bors#367).

CC ````@RalfJung````

r? ````@oli-obk````

Author: jieyouxu