
**Apache Airflow version**:
2.0.0

**Environment**:

- **OS** (e.g. from /etc/os-release): Ubuntu 20.04 LTS
- **Python version**: 3.8
- **Kernel** (e.g. `uname -a`): x86_64 x86_64 x86_64 GNU/Linux 5.4.0-58-generic #64-Ubuntu
- **Install tools**: pip


**What happened**:

Airflow 2.0 does not send metrics to statsD.

I configure Airflow with official documentation (https://airflow.apache.org/docs/apache-airflow/stable/logging-monitoring/metrics.html) and by this article https://dstan.medium.com/run-airflow-statsd-grafana-locally-16b372c86524 (but I used port 8125). 

I turned on statsD:

```ini
statsd_on = True
statsd_host = localhost
statsd_port = 8125
statsd_prefix = airflow
```

But I do not see airflow metrics at http://localhost:9102/metrics (statsD metrics endpoint).

---

P.S. I noticed this error just using Airflow 2.0. In version 1.10.13 everything is ok in the same environment.

Thank you for advance.



tests/core/test_stats.py
def setUp(self):
        self.dogstatsd_client = Mock()
        self.dogstatsd = SafeDogStatsdLogger(self.dogstatsd_client)
    def test_increment_counter_with_valid_name_with_dogstatsd(self):
        self.dogstatsd.incr('test_stats_run')
        self.dogstatsd_client.increment.assert_called_once_with(
            metric='test_stats_run', sample_rate=1, tags=[], value=1
        )
    def test_stat_name_must_be_a_string_with_dogstatsd(self):
        self.dogstatsd.incr([])
        self.dogstatsd_client.assert_not_called()
    def test_stat_name_must_not_exceed_max_length_with_dogstatsd(self):
        self.dogstatsd.incr('X' * 300)
        self.dogstatsd_client.assert_not_called()
    def test_stat_name_must_only_include_allowed_characters_with_dogstatsd(self):
        self.dogstatsd.incr('test/$tats')
        self.dogstatsd_client.assert_not_called()
    @conf_vars({('metrics', 'statsd_datadog_enabled'): 'True'})
    @mock.patch("datadog.DogStatsd")
    def test_does_send_stats_using_dogstatsd_when_dogstatsd_on(self, mock_dogstatsd):
        importlib.reload(airflow.stats)
        airflow.stats.Stats.incr("dummy_key")
        mock_dogstatsd.return_value.increment.assert_called_once_with(
            metric='dummy_key', sample_rate=1, tags=[], value=1
        )
    @conf_vars({('metrics', 'statsd_datadog_enabled'): 'True'})
    @mock.patch("datadog.DogStatsd")
    def test_does_send_stats_using_dogstatsd_with_tags(self, mock_dogstatsd):