[cv] update allow group for diagnostic API.
[cv] update allow group for diagnostic API.

R=vadimsh, yiwzhang

Bug: 1183616
Change-Id: Ie8a36997382ff1ff5a189a02784244560760df5b
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2727332
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Auto-Submit: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go