Auto merge of #140909 - fmease:modern-notif-backport-rustdoc, r=apiraino

Use new form for T-rustdoc's {beta,stable}-{nominated,accepted} notify-Zulip triggers

Applies [#t-rustdoc > PSA: New actions on backport notifs @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/PSA.3A.20New.20actions.20on.20backport.20notifs/near/514823133).
Complements #140397.

r? `@apiraino` or T-triagebot