dashboard: set a GO_TEST_TIMEOUT_SCALE for darwin-amd64-race

For golang/go#55311.

Change-Id: Ic708e37a15bc4f4afc3e80fa3c3d544c421f70d3
Reviewed-on: https://go-review.googlesource.com/c/build/+/500015
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

dashboard/builders.go

@@ -2679,6 +2679,16 @@ func init() {
 		HostType:       "host-darwin-amd64-12-aws",
 		distTestAdjust: macTestPolicy,
 		buildsRepo:     onlyGo,
+		env: []string{
+			// Increase the timeout scale for this builder: it was observed to be
+			// timing out frequently in
+			// https://go.dev/issue/55311#issuecomment-1571986012.
+			///
+			// TODO(bcmills): The darwin-amd64-longtest builder was running extremely
+			// slowly because it was hitting swap. Race-enabled builds are also
+			// memory-hungry — is it possible that the -race builder is also swapping?
+			"GO_TEST_TIMEOUT_SCALE=2",
+		},
 	})
 	addBuilder(BuildConfig{
 		Name:     "ios-arm64-corellium",