dumpsys: OWNERS for test

Now that we have it, we might move dumpsys_test over to using
libfakeservicemanager, but for now, I always have to edit this test when
I update the IServiceManager class. Hoping to save some CRs for it.

Bug: 185832616
Test: N/A
Change-Id: I778d3c8e8f4c0fa64640f6843da913df49e91d9d