Pulling this out of kubernetes/kubernetes#92937 (comment)

Related to but not explicitly part of #18551

One thing that's come up in discussion over why kubernetes PR's are so hard to merge (kubernetes/kubernetes#92937) is whether we really need so many jobs to run for each and every single PR that is opened against kubernetes/kubernetes. There is a desire to see if we can trim the number of jobs down without sacrificing (too much) coverage.

Reasons for this are:

• if we assume each job has a non-zero chance of flaking, fewer jobs means fewer chances for a PR to encounter a flake
• if we assume jobs are flaking due to resource contention, fewer jobs running means more resources available for jobs to consume

/priority important-soon
/area jobs
/sig testing
/sig release

FYI @BenTheElder @liggitt @kubernetes/ci-signal