### Apache Airflow version

main (development)

### What happened

Here's a dag:

```python3
from airflow import DAG
from airflow.decorators import task
import airflow.configuration as conf
from datetime import datetime

@task
def print_this(this):
    print(this)

with DAG(dag_id="config_ref", schedule=None, start_date=datetime(1970, 1, 1)) as dag:
    namespace = conf.get("kubernetes", "NAMESPACE")
    print_this(namespace)
```

In 2.4.3 it parses without error, but in main (as of 2e7a4bcb550538283f28550208b01515d348fb51) the reference to the "kubernetes" section breaks.  Likely because of this: https://github.com/apache/airflow/pull/26873
```
❯ airflow dags list-import-errors
filepath                              | error
======================================+========================================================================================================
/Users/matt/2022/11/29/dags/config.py | Traceback (most recent call last):
                                      |   File "/Users/matt/src/airflow/airflow/configuration.py", line 595, in get
                                      |     return self._get_option_from_default_config(section, key, **kwargs)
                                      |   File "/Users/matt/src/airflow/airflow/configuration.py", line 605, in _get_option_from_default_config
                                      |     raise AirflowConfigException(f"section/key [{section}/{key}] not found in config")
                                      | airflow.exceptions.AirflowConfigException: section/key  not found in config
                                      |

❯ python dags/config.py
[2022-11-29 21:30:05,300] {configuration.py:603} WARNING - section/key [kubernetes/namespace] not found in config
Traceback (most recent call last):
  File "/Users/matt/2022/11/29/dags/config.py", line 13, in <module>
    namespace = conf.get("kubernetes", "NAMESPACE")
  File "/Users/matt/src/airflow/airflow/configuration.py", line 1465, in get
    return conf.get(*args, **kwargs)
  File "/Users/matt/src/airflow/airflow/configuration.py", line 595, in get
    return self._get_option_from_default_config(section, key, **kwargs)
  File "/Users/matt/src/airflow/airflow/configuration.py", line 605, in _get_option_from_default_config
    raise AirflowConfigException(f"section/key [{section}/{key}] not found in config")
airflow.exceptions.AirflowConfigException: section/key [kubernetes/namespace] not found in config
```

To quote @jedcunningham :
>  The backcompat layer only expects you to use the “new” section name.




### What you think should happen instead

The recent section name change should be registered so that the old name still works.

### How to reproduce

See above

### Operating System

Mac OS / venv

### Versions of Apache Airflow Providers

n/a

### Deployment

Virtualenv installation

### Deployment details

`pip install -e ~/src/airflow` into a fresh venv

### Anything else

Also, it's kind of weird that the important part of the error message (which section?) is missing from `list-import-errors`.  I had to run the dag def like a script to realize that it was the kubernetes section that it was complaining about.


### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

self,
        config_sources: ConfigSourcesType,
        display_sensitive: bool,
        display_source: bool,
        raw: bool,
    ):
        for env_var in [
            os_environment for os_environment in os.environ if os_environment.startswith(ENV_VAR_PREFIX)
        ]:
            try:
                _, section, key = env_var.split("__", 2)
                opt = self._get_env_var_option(section, key)
            except ValueError:
                continue
            if opt is None:
                log.warning("Ignoring unknown env var '%s'", env_var)
                continue
            if not display_sensitive and env_var != self._env_var_name("core", "unit_test_mode"):