Looking in the source code it's clear that there's a build runner that is supposed to be running the rustls tests, however, it's difficult to actually find that build because it's not linked in Github's checks UI. Further the fact that Github checks reports ~45 different tests made me think that I just wasn't looking hard enough and it must be there somewhere.
The zuul builds are "screwed up" for the moment (#7522), as they are supposed to show up with a line among the CI builds like all the others but they don't and this is causing us big problems since we miss failed builds and more! I fear that we need to move over jobs from zuul to other services soon unless someone helps us fix this situation.
Otherwise I sympathize with your idea. Maybe we should move the CI specifics from CONTRIBUTE.d into a separate CI.md and work on populating it with all the info that should be there!?