The PATH variable is required to run the testenv tests.
Set it for all the runtime invocations where we don't
already set it by inheriting from the environment.
For #59583
For #59907
For #60097
Change-Id: If582dd8f086e3f40bc58d555f6034dcffe6f8e5f
Reviewed-on: https://go-review.googlesource.com/c/go/+/498616
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>