chromeos: Fix the exo_wlcs binary build

https://chromium-review.googlesource.com/c/chromium/src/+/5301923 moved
some calendar unit test utilities to the ash:test_support target. The
utilities have google_apis/calendar dependencies in their header, and
hence require google_apis/calendar as public_deps. It's not clear to
me why this was not caught by "gn check" on the original CL. With the
public_deps added, exo_wlcs now compiles.

Bug: 331226340
Test: autoninja -C out/Default exo_wlcs
Change-Id: Id177c196055491ba8212bba2f70b5562aa26cbb2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5398381
Auto-Submit: James Cook <jamescook@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278761}