tests: fix Whonix notifications interfering with test_300_bug_1028_gui_memory_pinning

Whonix Gateway shows some notifications / windows on startup (Tor
connection progress info, updates notification, news etc). When it
happens at the wrong time, it will switch focus between two screenshots,
affecting cursor image and thus causing the test to fail.

Avoid this by disabling starting Tor for this test.

Author: marmarek

qubes/tests/integ/vm_qrexec_gui.py

@@ -536,6 +536,8 @@ async def _test_300_bug_1028_gui_memory_pinning(self):
 
         # exclude from memory balancing
         self.testvm1.features['service.meminfo-writer'] = False
+        # prevent Whonix startup notifications from interfering
+        self.testvm1.features['service.whonix-tor-disable'] = True
         await self.testvm1.start()
         await self.wait_for_session(self.testvm1)