### 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)

#
#
#
from __future__ import annotations
import copy
import datetime
import io
import os
import re
import tempfile
import textwrap
import unittest
import warnings
from collections import OrderedDict
from unittest import mock
import pytest
from airflow import configuration
from airflow.configuration import (
    AirflowConfigException,
    AirflowConfigParser,
    conf,
    expand_env_var,