GitLab

Makes the error message more consistent between OAS and OAS2.

Fixes #26616.

Change-Id: I07ab46c5ef8a37efb2cb557632697f5d1bf789f7
Reviewed-on: https://go-review.googlesource.com/131280


Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>