cmd/go: don't run TestTestRaceInstall in short mode

Fixes #20158

Change-Id: Iefa9a33569eb805f5ab678d17c37787835bc7efa
Reviewed-on: https://go-review.googlesource.com/42134
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -2240,6 +2240,9 @@ func TestTestRaceInstall(t *testing.T) {
 	if !canRace {
 		t.Skip("no race detector")
 	}
+	if testing.Short() && testenv.Builder() == "" {
+		t.Skip("don't rebuild the standard library in short mode")
+	}
 
 	tg := testgo(t)
 	defer tg.cleanup()