Add more timeout for verify the interaction of the mock object

The verification happened earlier than the interaction with
production code. This may happen in low performance devices,
e.g. cuttlefish. Add timeout for the verification to deflake
the test.

Bug: 313828402
Test: atest FrameworksNetTests
Change-Id: I1ffa7e7573d503eb0396aa211a90ba032175b3a1
diff --git a/tests/unit/java/com/android/server/connectivity/VpnTest.java b/tests/unit/java/com/android/server/connectivity/VpnTest.java
index 46e9e45..c9cece0 100644
--- a/tests/unit/java/com/android/server/connectivity/VpnTest.java
+++ b/tests/unit/java/com/android/server/connectivity/VpnTest.java
@@ -2979,7 +2979,7 @@
                         null /* iface */, RTN_UNREACHABLE));
         assertEquals(expectedRoutes, lp.getRoutes());
 
-        verify(mMockNetworkAgent).unregister();
+        verify(mMockNetworkAgent, timeout(TEST_TIMEOUT_MS)).unregister();
     }
 
     @Test