ubuntu_performance_multipass failed with TypeError on Noble

[Po-Hsu Lin]

It looks like a python compatibility issue, test failed on Noble with:

    START ubuntu_performance_multipass.multipassboot ubuntu_performance_multipass.multipassboot timeout=1800 timestamp=1716332312 localtime=May 21 22:58:32
Persistent state client._record_indent now set to 2
Persistent state client.unexpected_reboot now set to ('ubuntu_performance_multipass.multipassboot', 'ubuntu_performance_multipass.multipassboot')
Waiting for pid 6564 for 1800 seconds
System python is too old, crash handling disabled
Running 'multipass list'
[stdout] Name State IPv4 Image
[stdout] test0xenial Running 10.71.127.110 Ubuntu 16.04 LTS
Running 'multipass exec test0xenial -- uname -r'
[stdout] 4.4.0-210-generic
Running 'multipass exec test0xenial -- systemd-analyze'
[stdout] Startup finished in 3.604s (kernel) + 33.197s (userspace) = 36.801s
Exception escaping from test:
Traceback (most recent call last):
  File "/home/ubuntu/autotest/client/shared/test.py", line 823, in _call_test_function
    return func(*args, **dargs)
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/autotest/client/shared/test.py", line 290, in execute
    self._call_run_once(constraints, profile_only,
  File "/home/ubuntu/autotest/client/shared/test.py", line 212, in _call_run_once
    self.run_once(*args, **dargs)
  File "/home/ubuntu/autotest/client/tests/ubuntu_performance_multipass/ubuntu_performance_multipass.py", line 228, in run_once
    keys = keys + result.keys()
           ~~~~~^~~~~~~~~~~~~~~
TypeError: can only concatenate list (not "dict_keys") to list