dashboard: set GO_TEST_TIMEOUT_SCALE for the riscv64 builder

It's slow like arm/mips/etc apparently.

Change-Id: I7638f22100d3af29cdcf7852701a3d4c8c8fc1d5
Reviewed-on: https://go-review.googlesource.com/c/build/+/217758
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index ad19615..0425cd4 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -2291,6 +2291,7 @@
 		HostType:     "host-linux-riscv64-unleashed",
 		Name:         "linux-riscv64-unleashed",
 		SkipSnapshot: true,
+		env:          []string{"GO_TEST_TIMEOUT_SCALE=4"},
 		shouldRunDistTest: func(distTest string, isTry bool) bool {
 			switch distTest {
 			case "api", "reboot":