net/http: Transport.CancelRequest no longer cancels in-flight request [1.14 backport] #41016
Description
@dmitshur requested issue #40453 to be considered for backport to the next 1.14 minor release.
@gopherbot Please backport to Go 1.14.
This is a second fixup to a previous fix (CL 242117) for an approved backport issue #39279. We can't submit that CL without this one (and #40973). This needs to be backported to Go 1.14 only, since the fix is already included in Go 1.15.