Ignore VolumeDialogImplTest

Suspected root cause of b/436170665 (interfering with other tests by not
successfully cleaning up messages in the handler). The class it's
testing is no longer used (though the flag isn't removed yet), so ignore
the test for now.

Bug: 436170665
Test: atest
Flag: EXEMPT bugfix
Change-Id: I7004ce90225883b82015addfefa8ca13fbc16f6f