testing: b.Loop gives bogus results in some situations [1.24 backport] #72974
Description
@aclements requested issue #72971 to be considered for backport to the next 1.24 minor release.
@gopherbot, please open a backport to Go 1.24.
I'm on the fence about whether this should be backported. It makes
b.Loop, which is new in Go 1.24, more robust to user mistakes, but those same mistakes could have been made with the oldb.Nstyle benchmarks, we just couldn't catch them. In support of backporting, it is a brand new feature and we're going to post a blog post about it soon so it'll probably get a spike in usage.