text/template: check ignored error in a test
text/template: check ignored error in a test

Found with staticcheck. Not terribly important since the test would
likely fail anyway, but at least it will fail with a better explanation
now.

Change-Id: Ic3f9a94a2152404b7873cc8cd47b6db79d78c2e6
Reviewed-on: https://go-review.googlesource.com/62990
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/go,cloudflare/go,josharian/go,polyverse-security/go,CAFxX/go,josharian/go,codestation/go,nawawi/go,CAFxX/go,polyverse-security/go,Cofyc/go,nawawi/go,codestation/go,polyverse-security/go,Cofyc/go,Cofyc/go,akutz/go,codestation/go,polyverse-security/go,nawawi/go,codestation/go,golang/go,golang/go,golang/go,cloudflare/go,CAFxX/go,golang/go,golang/go,golang/go,CAFxX/go,codestation/go,Cofyc/go,josharian/go,josharian/go,CAFxX/go,nawawi/go,polyverse-security/go,akutz/go,akutz/go,polyverse-security/go,codestation/go,CAFxX/go,cloudflare/go,codestation/go,CAFxX/go,josharian/go,josharian/go,Cofyc/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,josharian/go,codestation/go,akutz/go,nawawi/go,polyverse-security/go,cloudflare/go,Cofyc/go,akutz/go,Cofyc/go,cloudflare/go,josharian/go,akutz/go,cloudflare/go,akutz/go,akutz/go,Cofyc/go,christopher-henderson/Go,cloudflare/go,nawawi/go,polyverse-security/go,nawawi/go