[ci] wait for at least four minutes (#6878)
[ci] wait for at least four minutes (#6878)

Spinning up a VM takes around two minutes. Downloading fresh container images
takes additional time, maybe a whole minute.

The cost of timing out is high: an otherwise passing PR test run may fail
demanding a bump and delaying merging of said PR by fifteen to twenty minutes.

The cost of waiting two more minutes is that a resource deadlock may last
two extra minutes. We address deadlocks by scaling up and limiting concurrent
PR tests to four.
cseed/hail,hail-is/hail,danking/hail,hail-is/hail,cseed/hail,danking/hail,cseed/hail,cseed/hail,hail-is/hail,danking/hail,danking/hail,hail-is/hail,hail-is/hail,cseed/hail,cseed/hail,danking/hail,cseed/hail,danking/hail,hail-is/hail,cseed/hail,danking/hail,hail-is/hail,danking/hail,hail-is/hail