cmd/go: rank errUseProxy lower when handling proxy errors
modfetch.TryProxies ranks errors returned by GOPROXY entries by
usefulness. It returns the error of the highest rank from the last
proxy. Errors from "direct" and "noproxy" are most useful, followed by
errors other than ErrNotExist, followed by ErrNotExist.
This change ranks errUseProxy with ErrNotExist even though it's
reported by "noproxy". There is almost always a more useful message
than "path does not match GOPRIVATE/GONOPROXY".
Fixes #39180
Change-Id: Ifa5b96462d7bf411e6d2d951888465c839d42471
Reviewed-on: https://go-review.googlesource.com/c/go/+/234687
Run-TryBot: Jay Conrod <jayconrod@google.com> Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>