Disable ProcessObserverTest.testNormal

The ProcessObserver functionality for reporting started processes was
disabled, which causes the associated test to fail.  This change
disables the test.

Flag: EXEMPT bugfix
Bug: 323925686
Test: atest
 * FrameworksMockingServicesTests:com.android.server.am
Change-Id: Ic0d9332dc3ac7db746c38f73cf27e69b7d5ce9c1