tests/test_py3: fix deprecated loop arg

The loop arg has been removed in python 3.10. The same event loop will
be used without passing the argument, so it can be removed.

Fix for:
  TypeError: gather() got an unexpected keyword argument 'loop'

Related: https://stackoverflow.com/a/60315290
Related: https://docs.python.org/3/library/asyncio-task.html#asyncio.gather
Change-Id: I776bc463246e7a1a9adbb7c06012353d65694507

tests/test_py3.py

@@ -46,7 +46,7 @@ if __name__ == '__main__':
     print('Serving on {}...'.format(server.sockets[0].getsockname()))
 
     # Async client running in the subprocess plugged to the same event loop
-    loop.run_until_complete(asyncio.gather(asyncio.create_subprocess_exec('./scripts/osmo_ctrl.py', '-g', 'mnc', '-d', test_host, '-p', test_port), loop = loop))
+    loop.run_until_complete(asyncio.gather(asyncio.create_subprocess_exec('./scripts/osmo_ctrl.py', '-g', 'mnc', '-d', test_host, '-p', test_port)))
 
     loop.run_forever()