Reland "[roll_to_dev] Use a single push command for commits and tag"

This reverts commit 652561267133ebf049f1cd72b86ac74562edcc03.

Reason: using --atomic should fix the pushes (b/169389802#comment14).
Change-Id: Ibb74c461a3ae924c5a8337ba3ed28c74e4e68bef
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/167580
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: William Hesse <whesse@google.com>
Auto-Submit: Alexander Thomas <athom@google.com>
2 files changed