net/http: fix some test flakes caused by test refactoring
net/http: fix some test flakes caused by test refactoring

Skip TestTransportPersistConnLeakShortBody in HTTP/2 mode;
it's flaky and was previously HTTP/1-only.

Don't run TestTransportEventTrace and TestTransportIgnores408
in parallel.

Change-Id: I76bc540fac9317185ef7d414c9deafb35bc926b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/442495
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go