`crates/create_update_cl.py`: Support for updating a single crate.

Bug: 40221377
Change-Id: I68cd798ef405e6c6aff7657187e674a7b3ecb2dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5379194


Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277005}