dashboard: increase GO_TEST_TIMEOUT_SCALE for dragonfly builders
dashboard: increase GO_TEST_TIMEOUT_SCALE for dragonfly builders

This sets the GO_TEST_TIMEOUT_SCALE=2 for dragonfly builders in order
to try to solve intermittent test failures.

For golang/go#45215.
For golang/go#34034.
Fixes golang/go#45216.

Change-Id: I81dae533c137ff1903bf6b1a52cf9752e8921b7c
GitHub-Last-Rev: 9b4fb8017baebab4126a9d318f14f707eea79f9a
GitHub-Pull-Request: golang/build#35
Reviewed-on: https://go-review.googlesource.com/c/build/+/315329
Run-TryBot: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Trust: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>

golang/build,golang/build,golang/build,golang/build