Fix the check for release note files that correspond to API files
to look in the right directory, doc/next/*stdlib/*minor. Previously
the test looked in doc/next.
Improve the error messages when the test fails to explain the problem
better and refer to further documentation.
(These changes are actually in the x/build repo; this CL vendors
the latest version.)
Lastly, re-enable the check.
For #64169.
Change-Id: I8bba845e9bd12afbe269ce42d6d4b17b1e3c0252
Reviewed-on: https://go-review.googlesource.com/c/go/+/560516 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>