[BUG]: Important CI failures are not team-visible

[rwgk]

In passing I noticed that nightly CI: pixi run test is currently failing, but apparently there are no team-visible failure notifications set up for this workflow. We should fix that.

[leofang]

There are many kinds of nightly runs that we have now, not just pixi. In addition, if the CI on the main branch fails, we don't get notification either. I've been handling such cases casually since the dawn of this team (clicking re-runs every night before signing off and fixing any real errors as soon as I see them).

We can build a notification mechanism and I believe both CCCL and RAPIDS have enough code that we can just steal and jump start, but we should do this holistically for all CI pipelines instead of any particular one.

[rwgk]

I changed the issue title to be more general. (I'm assuming the incremental effort to apply the notification mechanism to multiple pipelines is very small.)