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
@staticmethod
    def _prepare_test_file(filepath: str, size: int):
        os.makedirs(os.path.dirname(filepath), exist_ok=True)
        with open(filepath, "w") as file:
            file.write("A" * size)
            file.flush()
    def test_should_detect_changes_in_directory(self):
        with tempfile.TemporaryDirectory() as tempdir,\
             mock.patch("airflow.cli.commands.webserver_command.settings.PLUGINS_FOLDER", tempdir):
            self._prepare_test_file(f"{tempdir}/file1.txt", 100)
            self._prepare_test_file(f"{tempdir}/nested/nested/nested/nested/file2.txt", 200)
            self._prepare_test_file(f"{tempdir}/file3.txt", 300)
            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,
            )
            
            state_a = monitor._generate_plugin_state()
            state_b = monitor._generate_plugin_state()
            self.assertEqual(state_a, state_b)
            self.assertEqual(3, len(state_a))
            
            self._prepare_test_file(f"{tempdir}/file4.txt", 400)