iotests/231: Update expected deprecation message

iotests/231: Update expected deprecation message

The deprecation message in the expected output has technically been
wrong since the wrong version of a patch was applied to it. Because of
this, the test fails. Correct the expected output so that it passes.

Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20210421212343.85524-2-ckuehl@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>