Now that the CQ has been enabled for both the Beta and Stable
branches, git-drover should use the commit queue instead of
directly submitting the CL. To that end, this CL replaces the
usage of `git cl land` with `git cl set-commit`.

Change-Id: I0d0c10115acc98eafe0c069825de5499b8ade3e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1960697
Auto-Submit: Aaron Gable <agable@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>