net: skip TestLookupGmailTXT on Plan 9
net: skip TestLookupGmailTXT on Plan 9

CL 157638 updated TestLookupGmailTXT. However, this
test is failing on Plan 9, because the DNS resolver
(ndb/dns) only returns a single TXT record.

Updates #29722.

Change-Id: I01cd94e6167902361c3f5d615868f6f763a31fb1
Reviewed-on: https://go-review.googlesource.com/c/157737
Run-TryBot: David du Colombier <ec8ae1e6620d4bab5e0e7aa2a6ae41aad63e3708@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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