This will print a warning and disable new auth if .gitcookies file
exists.
This ensures we don't break bots once we default new auth on while
pushing human users away from .gitcookies.
Bug: b/404613530
Change-Id: Ia2d05bb7e5d2bf11e5605a26ef492954acbd9833
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6367723
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Allen Li <ayatane@chromium.org>