go/doc: add a golden test that reproduces #62640

go/doc: add a golden test that reproduces #62640

For #62640.
For #61394.

This is a copy of https://go-review.googlesource.com/c/go/+/528402,
which has stalled in review and the owner is no longer working on Go.

Change-Id: Ic7a1ae65c70d4857ab1061ccae1a926bf5c4ff55
Reviewed-on: https://go-review.googlesource.com/c/go/+/681235
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>