tests: test_wizard: fix warnings

```
=============================== warnings summary ===============================
tests/test_wizard.py::ServerConnectWizardTestCase::test_no_advanced
tests/test_wizard.py::ServerConnectWizardTestCase::test_proxy
tests/test_wizard.py::ServerConnectWizardTestCase::test_proxy_and_server
tests/test_wizard.py::ServerConnectWizardTestCase::test_server
tests/test_wizard.py::WalletWizardTestCase::test_2fa
tests/test_wizard.py::WalletWizardTestCase::test_create_standard_wallet_haveseed_bip39
tests/test_wizard.py::WalletWizardTestCase::test_create_standard_wallet_haveseed_electrum
tests/test_wizard.py::WalletWizardTestCase::test_create_standard_wallet_newseed
  /tmp/cirrus-ci-build/.tox/py3/lib/python3.10/site-packages/_pytest/threadexception.py:82: PytestUnhandledThreadExceptionWarning: Exception in thread Plugins

  Traceback (most recent call last):
    File "/usr/local/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
      self.run()
    File "/tmp/cirrus-ci-build/electrum/plugin.py", line 360, in run
      self.on_stop()
    File "/tmp/cirrus-ci-build/electrum/util.py", line 430, in on_stop
      loop = get_asyncio_loop()
    File "/tmp/cirrus-ci-build/electrum/util.py", line 1578, in get_asyncio_loop
      raise Exception("event loop not created yet")
  Exception: event loop not created yet

    warnings.warn(pytest.PytestUnhandledThreadExceptionWarning(msg))
```

tests/test_wizard.py

@@ -46,9 +46,9 @@ class WizardTestCase(ElectrumTestCase):
         self.plugins.load_internal_plugin('trustedcoin')
 
     def tearDown(self):
-        super().tearDown()
         self.plugins.stop()
         self.plugins.stopped_event.wait()
+        super().tearDown()
 
 
 class ServerConnectWizardTestCase(WizardTestCase):