cmd/go: only print GOCACHE value in env -changed if it's not the default
When other environment variables are set to default values,
we will not print it in go env -changed,
GOCACHE should do the same.
For #69994
Change-Id: I16661803cf1f56dd132b4db1c2d5cb4823fc0e58
Reviewed-on: https://go-review.googlesource.com/c/go/+/621997 Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>