### 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)

"""
    Ensure that all secrets backends are loaded.
    If the secrets_backend_list contains only 2 default backends, reload it.
    """
    
    if len(secrets_backend_list) == 2:
        return initialize_secrets_backends()
    return secrets_backend_list
def get_custom_secret_backend() -> BaseSecretsBackend | None:
    """Get Secret Backend if defined in airflow.cfg."""
    secrets_backend_cls = conf.getimport(section="secrets", key="backend")
    if not secrets_backend_cls:
        return None
    try:
        backend_kwargs = conf.getjson(section="secrets", key="backend_kwargs")
        if not backend_kwargs:
            backend_kwargs = {}
        elif not isinstance(backend_kwargs, dict):
            raise ValueError("not a dict")
    except AirflowConfigException:
        log.warning("Failed to parse [secrets] backend_kwargs as JSON, defaulting to no kwargs.")
        backend_kwargs = {}
    except ValueError:
        log.warning("Failed to parse [secrets] backend_kwargs into a dict, defaulting to no kwargs.")
        backend_kwargs = {}
    return secrets_backend_cls(**backend_kwargs)
def initialize_secrets_backends() -> list[BaseSecretsBackend]: