go/types: enable disabled test for comma-ok expressions
go/types: enable disabled test for comma-ok expressions

This was fixed long ago but the test was not enabled.

For #8189.

Change-Id: Ia44ef752b6bf076f3e243d2d0db326a392a20193
Reviewed-on: https://go-review.googlesource.com/27310
Run-TryBot: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

CAFxX/go,akutz/go,vsekhar/elastic-go,vsekhar/elastic-go,polyverse-security/go,akutz/go,polyverse-security/go,momchil-velikov/go,cloudflare/go,codestation/go,ImJasonH/go,linux-on-ibm-z/go,ImJasonH/go,akutz/go,nawawi/go,codestation/go,josharian/go,Cofyc/go,CAFxX/go,cloudflare/go,goodlang/good,suncycheng/go,Cofyc/go,akutz/go,ImJasonH/go,josharian/go,goodlang/good,momchil-velikov/go,golang/go,vsekhar/elastic-go,suncycheng/go,Cofyc/go,cloudflare/go,golang/go,linux-on-ibm-z/go,josharian/go,linux-on-ibm-z/go,derekmarcotte/go,golang/go,codestation/go,codestation/go,vsekhar/elastic-go,cloudflare/go,linux-on-ibm-z/go,akutz/go,momchil-velikov/go,Cofyc/go,cloudflare/go,polyverse-security/go,momchil-velikov/go,christopher-henderson/Go,polyverse-security/go,goodlang/good,momchil-velikov/go,derekmarcotte/go,suncycheng/go,nawawi/go,Cofyc/go,golang/go,polyverse-security/go,suncycheng/go,goodlang/good,CAFxX/go,josharian/go,suncycheng/go,codestation/go,cloudflare/go,nawawi/go,josharian/go,derekmarcotte/go,codestation/go,CAFxX/go,nawawi/go,linux-on-ibm-z/go,ImJasonH/go,cloudflare/go,goodlang/good,goodlang/good,Cofyc/go,polyverse-security/go,CAFxX/go,CAFxX/go,vsekhar/elastic-go,polyverse-security/go,ImJasonH/go,ImJasonH/go,ImJasonH/go,suncycheng/go,golang/go,nawawi/go,momchil-velikov/go,josharian/go,suncycheng/go,golang/go,momchil-velikov/go,golang/go,linux-on-ibm-z/go,ImJasonH/go,vsekhar/elastic-go,suncycheng/go,codestation/go,derekmarcotte/go,codestation/go,polyverse-security/go,goodlang/good,akutz/go,derekmarcotte/go,vsekhar/elastic-go,Cofyc/go,golang/go,cloudflare/go,derekmarcotte/go,nawawi/go,linux-on-ibm-z/go,josharian/go,CAFxX/go,CAFxX/go,josharian/go,linux-on-ibm-z/go,derekmarcotte/go,Cofyc/go,nawawi/go,momchil-velikov/go,vsekhar/elastic-go,nawawi/go,akutz/go,goodlang/good,derekmarcotte/go,akutz/go