### Apache Airflow version

2.2.0b2 (beta snapshot)

### Operating System

Debian buster

### Versions of Apache Airflow Providers

_No response_

### Deployment

Astronomer

### Deployment details

Astro dev start

### What happened

Unable to change username while updating user information through API though it's possible from UI.

### What you expected to happen

Either username should not be editable from UI or It should be editable from API.

### How to reproduce

1. Use a patch request with the below URL.
`{{url}}/users/{{username}}`
2. In payload use a different username
```
 {
        "username": "{{username1}}",
        "password": "password1",
        "email": "{{email}}@example.com",
        "first_name": "{{$randomFirstName}}",
        "last_name": "{{$randomLastName}}",
        "roles":[{ "name": "Op"}]
}
```


### Anything else

_No response_

### 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)

airflow/api_connexion/endpoints/user_endpoint.py
"""Delete a user"""
    security_manager = current_app.appbuilder.sm
    user = security_manager.find_user(username=username)
    if user is None:
        detail = f"The User with username `{username}` was not found"
        raise NotFound(title="User not found", detail=detail)
    user.roles = []  
    security_manager.get_session.delete(user)
    security_manager.get_session.commit()