cmd/go: in TestScript/gotoolchain_path, remove the user's PATH
This test checks a behavior of GOTOOLCHAIN when an appropriate
toolchain is found in PATH. That requires it to exclude any suitable
toolchain binaries from the user's $PATH, which may otherwise
interfere.
Fixes #62709.
Change-Id: Ie9161e52d33a65be0b5265cb49e9f2bc8473e057
Reviewed-on: https://go-review.googlesource.com/c/go/+/529217
Auto-Submit: Bryan Mills <bcmills@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>