http2: disable TLS 1.3 in failing test temporarily(?)
http2: disable TLS 1.3 in failing test temporarily(?)

Updates golang/go#28762

Change-Id: If73b292f28e553646431af995942169ce58d43f5
Reviewed-on: https://go-review.googlesource.com/c/149357
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/net