BeanieBaseUserDocument unique email index not being applied, multiple users with the same email in the database

Describe the bug

BeanieBaseUserDocument defines 2 indexes on the email field , one being a unique index and the other being a collation. However only the collation index is applied to the email field in the database. This means that multiple users with the same emaill can end up in the database.

To Reproduce

To make reproducing this simpler i have lifted the BeanieBaseUserDocument model directly from this repo and put it into a minimal example.

Model from https://github.com/fastapi-users/fastapi-users-db-beanie/blob/eedd1039cd8d3aece0f49fa1a90d9649ca80d1ee/fastapi_users_db_beanie/__init__.py#L16

import asyncio
from typing import Optional

from motor.motor_asyncio import AsyncIOMotorClient
from pydantic import BaseModel

from beanie import Document, Indexed, init_beanie
from pymongo import IndexModel
from pymongo.collation import Collation

class BeanieBaseUser(BaseModel):
    email: str
    hashed_password: str
    is_active: bool = True
    is_superuser: bool = False
    is_verified: bool = False

    class Settings:
        email_collation = Collation("en", strength=2)
        indexes = [
            IndexModel("email", unique=True),
            IndexModel(
                "email", name="case_insensitive_email_index", collation=email_collation
            ),
        ]

class BeanieBaseUserDocument(BeanieBaseUser, Document):  # type: ignore
    pass

async def example():
    client = AsyncIOMotorClient("mongodb://localhost:27017")
    await init_beanie(database=client.db_name, document_models=[BeanieBaseUserDocument])

    await BeanieBaseUserDocument(email="email@email.email",hashed_password="hashed_password").save()
    await BeanieBaseUserDocument(email="email@email.email",hashed_password="hashed_password1").save()

if __name__ == "__main__":
    asyncio.run(example())

The behavior is not as expected:

Instead of mongo complaining about the same email it allows multiple emails to be the same:
There is no unique index on the email field in the mongodb index list:

Expected behavior

The database should prevent duplicate emails from being added via the indexes.

Additional context

If you reverse the index definition order then the unique index works but the collation does not. Implying the second index takes precedence.
This can be fixed by putting the index definitions into a single definition like below:

class BeanieBaseUser(BaseModel):
    email: str
    hashed_password: str
    is_active: bool = True
    is_superuser: bool = False
    is_verified: bool = False

    class Settings:
        email_collation = Collation("en", strength=2)
        indexes = [
            IndexModel(
                "email", name="case_insensitive_email_index_unique", collation=email_collation, unique=True
            ),
        ]

Software versions

beanie 1.24.0

fastapi-users / fastapi-users-db-beanie