Still, opt-out is just inacceptable. At least with a mechanism which can easily fail, like setting an environment variable. This basically forces you to wrap the go tool in a script which ensures the environment variable to be set.
As this seem to cache the results, another option is to fiddle with the cache to report bogus information.
Yeah, given go's history with breaking changes (and the habit of OKR-chasing managers and Senior Staff to make Number Go Up to look good on the promo packet), I definitely would not trust any opt-out mechanism to not receive operationally-significant changes in the next five years.
As this seem to cache the results, another option is to fiddle with the cache to report bogus information.