Support main branch in bot_update
Support main branch in bot_update

Change-Id: I58e88e9505779c309ac0af9d5b78b45feaa75543
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2528669
Reviewed-by: Edward Lesmes <d05609f027dc667cc37492b1dc1bdea5d60fa82a@chromium.org>
Commit-Queue: Josip Sokcevic <4606aec58cba917397ff2e4738f995e4758694f8@google.com>

CoherentLabs/depot_tools,CoherentLabs/depot_tools