[base] Add altimin@ to //base/OWNERS

As approved offline.

R=altimin@chromium.org, danakj@chromium.org, dcheng@chromium.org, fdoray@chromium.org, mark@chromium.org

Change-Id: I8cddbdd01e9dade522b476a6eb70f83e93b91cd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3891610


Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1046029}