dashboard: expand time scale for windows-arm builder

This builder has very slow I/O and could benefit from some extra time on
a few tests. At the moment, the tests for x/review/git-codereview are
failing with a time out, for example.

Updates golang/go#42925.

Change-Id: I532f4ddd3b9e7fd0a66ea9631b3fa7ce363e05a4
Reviewed-on: https://go-review.googlesource.com/c/build/+/274572
Trust: Jason A. Donenfeld <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: zx2c4

dashboard/builders.go

@@ -2208,7 +2208,7 @@ func init() {
 		HostType: "host-windows-arm64-zx2c4",
 		env: []string{
 			"GOARM=7",
-			"GO_TEST_TIMEOUT_SCALE=2"},
+			"GO_TEST_TIMEOUT_SCALE=3"},
 	})
 	addBuilder(BuildConfig{
 		Name:     "darwin-amd64-10_11",