go/build: clarify that there are no build tags for minor releases
go/build: clarify that there are no build tags for minor releases

Fixes #26458

Change-Id: If932718ca8a2b230ab52495c1a7a82d86ab1325b
Reviewed-on: https://go-review.googlesource.com/136215
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

akutz/go,nawawi/go,josharian/go,cloudflare/go,CAFxX/go,CAFxX/go,josharian/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,golang/go,golang/go,josharian/go,golang/go,golang/go,CAFxX/go,CAFxX/go,josharian/go,josharian/go,CAFxX/go,CAFxX/go,nawawi/go,josharian/go,josharian/go,cloudflare/go,akutz/go,cloudflare/go,akutz/go,CAFxX/go,nawawi/go,josharian/go,golang/go,nawawi/go,akutz/go,akutz/go,cloudflare/go,cloudflare/go,golang/go,akutz/go,golang/go,akutz/go,cloudflare/go,nawawi/go,nawawi/go,akutz/go,nawawi/go