Fix flaky history job service test

I suspect this test flakes because it sets JobServiceEngine
via reflection, bypassing the proper construction of
JobServiceEngine (via JobService.onBind), which inits the
JobHandler that we need to get a non-null message.

Fixes: 302339170
Test: NotificationHistoryJobServiceTest
Change-Id: Ia7af0f2c2b96ecb6202369418b53a69d083982da