To pick up
https://chromium.googlesource.com/infra/luci/luci-go/+/df34c731

Without it CIPD deletes the current working directory when running
`cipd ensure -root <a-read-only-directory> ...` without
CIPD_CACHE_DIR set. Oops.

R=tandrii@chromium.org, iannucci@chromium.org
BUG=b/197679760

Change-Id: I8b2dfb8795d1ad4b46484c7baca520b03acc94e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3119606Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>