build: use multiScm for Kokoro release builds#981

gcf-owl-bot[bot] wants to merge 2 commits intomaingoogleapis/python-firestore:mainfrom

owl-bot-update-lock-5cddfe2fb5019bbf78335bc55f15bc13e18354a56b3ff46e1834f8e540807f05googleapis/python-firestore:owl-bot-update-lock-5cddfe2fb5019bbf78335bc55f15bc13e18354a56b3ff46e1834f8e540807f05Copy head branch name to clipboard