### 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

"Already exists." error message is missing while updating user email with existing email id through API.

### What you expected to happen

"Email id already exists" error message should appear

### How to reproduce

1. Use a patch request with the below URL.
`{{url}}/users/{{username}}`
2. In payload use an exiting email id 
```
 {
        "username": "{{username}}",
        "password": "password1",
        "email": "{{exiting_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)

tests/api_connexion/endpoints/test_user_endpoint.py
)
        assert response.status_code == 409, response.json
        error_detail = error_detail_template.format(username=existing.username, email=existing.email)
        assert response.json["detail"] == error_detail
    @pytest.mark.parametrize(
        "payload_converter, error_message",
        [
            pytest.param(
                lambda p: {k: v for k, v in p.items() if k != "username"},
                "{'username': ['Missing data for required field.']}",
                id="missing-required",
            ),
            pytest.param(
                lambda p: {"i-am": "a typo", **p},
                "{'i-am': ['Unknown field.']}",
                id="unknown-user-field",
            ),
            pytest.param(
                lambda p: {**p, "roles": [{"also": "a typo", "name": "User"}]},
                "{'roles': {0: {'also': ['Unknown field.']}}}",
                id="unknown-role-field",
            ),
            pytest.param(
                lambda p: {**p, "roles": [{"name": "God"}, {"name": "User"}, {"name": "Overlord"}]},
                "Unknown roles: 'God', 'Overlord'",
                id="unknown-role",
            ),
        ],
    )
    def test_invalid_payload(self, autoclean_user_payload, payload_converter, error_message):