✅ Change the transition for the negative test to one that actually fails

Our negative test in this test suite used `transition': none`
as an invalid transition. However, in
e-mission@c86fcf5
we started handling `None` transitions properly

So we need to change it to a transition that is actually invalid.

Testing done:
Before this, `testMoveWhenEmpty` failed.
Now, `testMoveWhenEmpty` passes

emission/tests/netTests/TestBuiltinUserCacheHandlerInput.py

@@ -138,7 +138,7 @@ def testMoveWhenEmpty(self):
         edb.get_usercache_db().insert_one({
             'user_id': self.testUserUUID1,
             '_id': boi.ObjectId('572d3621d282b8f30def7e85'),
-            'data': {u'transition': None,
+            'data': {u'transition': "MY_FAKE_TRANSITION",
                      'currState': u'STATE_ONGOING_TRIP'},
             'metadata': {'plugin': 'none',
                          'write_ts': self.curr_ts - 25,