internal/godebugs: test for use of IncNonDefault

internal/godebugs: test for use of IncNonDefault

A few recent godebugs are missing IncNonDefault uses.
Test for that, so that people remember to do it.
Filed bugs for the missing ones.

For #66215.
For #66216.
For #66217.

Change-Id: Ia3fd10fd108e1b003bb30a8bc2f83995c768fab6
Reviewed-on: https://go-review.googlesource.com/c/go/+/570275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>