We should keep a consistent way of formatting errors
in this file.

Fixes #34848

Change-Id: Ibb75908504f381fccab0281a42e788ef8c716b6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/200679
Run-TryBot: Johan Brandhorst <johan.brandhorst@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>