Rollup merge of #75496 - spastorino:prioritization-zulip-topics, r=Mark-Simulacrum

Rollup merge of #75496 - spastorino:prioritization-zulip-topics, r=Mark-Simulacrum

Prioritization WG: Open Zulip topics only for `I-prioritize` issues

This was discussed in https://rust-lang.zulipchat.com/#narrow/stream/227806-t-compiler.2Fwg-prioritization/topic/nominations.20and.20other.20automatically.20opened.20topics
Is not being helpful to open topics on any of these events and it's even causing more work for the group.

@LeSeulArtichaut ... I think this is all that's needed to get rid of this, right?.

r? @Mark-Simulacrum

cc @rust-lang/wg-prioritization

@bors rollup=always