git: openjdk/jdk11u-dev: 8274083: Update testing docs to mention tiered testing

[Aleksey Shipilev]

Changeset: 441b4de7
Author:    Aleksey Shipilev <shade at openjdk.org>
Date:      2021-10-07 06:55:42 +0000
URL:       https://git.openjdk.java.net/jdk11u-dev/commit/441b4de79c15182db0b894b7c47db4d7b9c07b9a

8274083: Update testing docs to mention tiered testing

Backport-of: 971aa353aae51222ca33ebfdd61b91672a6c871a

! doc/testing.html
! doc/testing.md