### 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
#
#
from flask import current_app, request
from flask_appbuilder.security.sqla.models import User
from marshmallow import ValidationError
from sqlalchemy import func
from werkzeug.security import generate_password_hash
from airflow.api_connexion import security
from airflow.api_connexion.exceptions import AlreadyExists, BadRequest, NotFound, Unknown
from airflow.api_connexion.parameters import apply_sorting, check_limit, format_parameters
from airflow.api_connexion.schemas.user_schema import (
    UserCollection,
    user_collection_item_schema,
    user_collection_schema,
    user_schema,
)
from airflow.security import permissions
@security.requires_access([(permissions.ACTION_CAN_READ, permissions.RESOURCE_USER)])
def get_user(username):