We have some random failures in teardown of TestCliWebServer.test_cli_webserver_foreground.

Since this is in teardown, it can be likely ignored because we are killing those background processes with -9 anyway.

https://github.com/apache/airflow/pull/11526/checks?check_run_id=1268530821#step:6:1193

```
________________ TestCliWebServer.test_cli_webserver_foreground ________________

self = <tests.cli.commands.test_webserver_command.TestCliWebServer testMethod=test_cli_webserver_foreground>

    def tearDown(self) -> None:
>       self._check_processes()

tests/cli/commands/test_webserver_command.py:247: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <tests.cli.commands.test_webserver_command.TestCliWebServer testMethod=test_cli_webserver_foreground>

    def _check_processes(self):
        # Confirm that webserver hasn't been launched.
        # pgrep returns exit status 1 if no process matched.
        exit_code_pgrep_webserver = subprocess.Popen(["pgrep", "-c", "-f", "airflow webserver"]).wait()
        exit_code_pgrep_gunicorn = subprocess.Popen(["pgrep", "-c", "-f", "gunicorn"]).wait()
        if exit_code_pgrep_webserver != 1 or exit_code_pgrep_gunicorn != 1:
            subprocess.Popen(["ps", "-ax"]).wait()
            if exit_code_pgrep_webserver != 1:
                subprocess.Popen(["pkill", "-9", "-f", "airflow webserver"]).wait()
            if exit_code_pgrep_gunicorn != 1:
                subprocess.Popen(["pkill", "-9", "-f", "gunicorn"]).wait()
    
            raise AssertionError(
>               "Background processes are running that prevent the test from passing successfully."
            )
E           AssertionError: Background processes are running that prevent the test from passing successfully.

tests/cli/commands/test_webserver_command.py:243: AssertionError
```
tests/cli/commands/test_webserver_command.py
state_c = monitor._generate_plugin_state()
            self.assertNotEqual(state_b, state_c)
            self.assertEqual(4, len(state_c))
            
            self._prepare_test_file(f"{tempdir}/file4.txt", 450)
            state_d = monitor._generate_plugin_state()
            self.assertNotEqual(state_c, state_d)
            self.assertEqual(4, len(state_d))
            
            self._prepare_test_file(f"{tempdir}/file4.txt", 4000000)
            state_d = monitor._generate_plugin_state()
            self.assertNotEqual(state_c, state_d)
            self.assertEqual(4, len(state_d))
class TestCLIGetNumReadyWorkersRunning(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        cls.parser = cli_parser.get_parser()
    def setUp(self):
        self.children = mock.MagicMock()
        self.child = mock.MagicMock()
        self.process = mock.MagicMock()
        self.monitor = GunicornMonitor(
            gunicorn_master_pid=1,
            num_workers_expected=4,
            master_timeout=60,
            worker_refresh_interval=60,
            worker_refresh_batch_size=2,
            reload_on_plugin_change=True,
        )
    def test_ready_prefix_on_cmdline(self):