html/template: fix typo in TestOrphanedTemplate error message

This error message should reference t2, not t1.

Change-Id: I2e42b8335ca9367a1fb7f76c38a1bcf8f32a2bf3
Reviewed-on: https://go-review.googlesource.com/82816Reviewed-by: Gabriel Aszalos <gabriel.aszalos@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Gabriel Aszalos <gabriel.aszalos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/html/template/escape_test.go

@@ -1918,7 +1918,7 @@ func TestOrphanedTemplate(t *testing.T) {
 	}
 	b.Reset()
 	if err := t2.Execute(&b, nil); err != nil {
-		t.Fatalf("error executing t1: %s", err)
+		t.Fatalf("error executing t2: %s", err)
 	}
 	const want = "bar"
 	if got := b.String(); got != want {