internal/proxy: fix error reporting

We weren't reporting on NotFound, but the right code is NotFetched,
since that is what is returned when proxy fetch is disabled.

Change-Id: I554d5186fb4db0346fb9456fe9fc55091066abda
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/320751
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

internal/proxy/client.go

@@ -98,8 +98,11 @@ func (c *Client) WithZipCache() *Client {
 // endpoint instead.
 func (c *Client) Info(ctx context.Context, modulePath, requestedVersion string) (_ *VersionInfo, err error) {
 	defer func() {
+		// Don't report NotFetched, because it is the normal result of fetching
+		// an uncached module when fetch is disabled.
+		// Don't report timeouts, because they are relatively frequent and not actionable.
 		wrap := derrors.Wrap
-		if !errors.Is(err, derrors.NotFound) && !errors.Is(err, derrors.ProxyTimedOut) {
+		if !errors.Is(err, derrors.NotFetched) && !errors.Is(err, derrors.ProxyTimedOut) {
 			wrap = derrors.WrapAndReport
 		}
 		wrap(&err, "proxy.Client.Info(%q, %q)", modulePath, requestedVersion)