cmd/go: address code review comments in test cgo_path_space_quote

For CL 334732.

Change-Id: I5cb88cd7d5e4edf6006bbaeb17723dac2cdf0fd5
Reviewed-on: https://go-review.googlesource.com/c/go/+/339590


Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/341938