go/packages: fix broken test that checks errors
go/packages: fix broken test that checks errors

Change-Id: Id9b1dc5e01a5b7eeca45448be0b7d7eef79fa928
Reviewed-on: https://go-review.googlesource.com/c/tools/+/172400
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Reviewed-by: Ian Cottrell <52376736e5e84615ec49f9c1843b8acc178b1d8d@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools