cmd/go/internal/modfetch/codehost: report git errors more accurately
Previously, if you attempted to fetch a private repository, or your
Git/curl client failed for an unknown reason, codehost would return an
UnknownRevisionError, which reported that a given revision in go.mod
was "unknown". This is confusing to many users who can go look in
their browser for example and see that the commit-ish exists.
Instead check whether "git ls-remote" exited with an error, and if so,
return that instead of the UnknownRevision message.
Fixes #42751.
Change-Id: I0dbded878b2818280e61126a4493767d719ad577
Reviewed-on: https://go-review.googlesource.com/c/go/+/297950 Reviewed-by: Bryan C. Mills <bcmills@google.com>
Trust: Bryan C. Mills <bcmills@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>