cmd/go: fix sumdb test failure with misbehaving DNS server

Broadened the regular expression used to test error messages for
failing to connect to "localhost.localdev/sumdb". Some DNS servers
resolve unknown domains like "localhost.localdev" to real IP addresses
to serve ads. We may get a variety of error messages.

Fixes #31779

Change-Id: Ib389c633c9a9f70f8e89bbcba5282a375da4e708
Reviewed-on: https://go-review.googlesource.com/c/go/+/182799


Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>