[Android] Disable flaky FirstRunActivitySigninAndSyncTest tests

The test suite is generally flaky and in particular on Android Nougat.

Bug: 1459076
Change-Id: Ia1def8c2f9a3a2f0937c3e3af893b9890ce3deaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4754739


Commit-Queue: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1180611}