go/types, types2: fix failing error message test for s390x

go/types, types2: fix failing error message test for s390x

Fixes #73206.

Change-Id: If27ce5fe7aa71415b6e2d525c78b1f04b88a308b
Reviewed-on: https://go-review.googlesource.com/c/go/+/663635
TryBot-Result: Gopher Robot <gobot@golang.org>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Mark Freeman <mark@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>