cmd/go: add go command known variables to test cache hash

The go test result must not be cached when each of known variables to go
command change.

To do this, add all known variables to test metadata.

Fixes #32285

Change-Id: I90be6a72f46c42d965aec4fed534c0623244cd3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/179040


Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>