runtime: correctly log stderr in TestFakeTime

Change-Id: Iaf122ce7a8b8fb431199399aeed67b128a34d20b
Reviewed-on: https://go-review.googlesource.com/c/go/+/255720
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/runtime/time_test.go b/src/runtime/time_test.go
index bf29561..a8dab7d 100644
--- a/src/runtime/time_test.go
+++ b/src/runtime/time_test.go
@@ -38,7 +38,7 @@
 	}
 
 	t.Logf("raw stdout: %q", stdout.String())
-	t.Logf("raw stderr: %q", stdout.String())
+	t.Logf("raw stderr: %q", stderr.String())
 
 	f1, err1 := parseFakeTime(stdout.Bytes())
 	if err1 != nil {