misc/cgo/testcarchive: fix `go env` error message
misc/cgo/testcarchive: fix `go env` error message

Add a missing newline.  Don't panic on an unexpected error type.

Change-Id: I82a4b12c498fbfdf4972737329631c0c02540005
Reviewed-on: https://go-review.googlesource.com/44092
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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