[linux-lacros-rel dangling ptr] Fix RemoteAppsProxyLacrosUnittest

Bug: 324461153
Change-Id: Ie49d58b0680981e80bb4f2c633aa2e8c70af43df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5336166


Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: pengchao Cai <pengchaocai@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1267516}