The enforce_fetch kwarg was being ignored. This change adds the
--enforce_fetch to the resources/bot_update cmd.
Confirmed here through led: https://logs.chromium.org/logs/chromium/led/kimstephanie_google.com/b852fa5e4bd75b11d2dfd35bb66caa5147698ad1b77d6fb2aa69ec87ee57b5d2/+/steps/bot_update/0/logs/execution_details/0

Bug: 1129235
Change-Id: I78c5d62841fda6dafbb709301e26c5047df2d58d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2444114Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>