cit.py: Use infra.git's cit branch instead of the deployed branch
cit.py: Use infra.git's cit branch instead of the deployed branch

So that we can roll the cit.py pin without breaking other services.

BUG=

Change-Id: I5992d753d8ddf23c29f1ef6c09866a86c7f7c2ae
Reviewed-on: https://chromium-review.googlesource.com/450760
Reviewed-by: Daniel Jacques <8400006a9338a0893dca0101ad49838955bd6b2c@chromium.org>
Commit-Queue: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools