[BUG] Bunnet update doesn't have the same behavior as beanie's update

[stefan-jiroveanu]

Describe the bug
So if I am trying to run update for sync operations, using bunnet I need to use pydantic by_alias inside model_dump, while for beanie I don't need to do that.

Under the hood, I think the async Beanie update path and the sync Bunnet update path actually behave differently when it comes to your field‐name ↔ Mongo‐alias mapping.

To Reproduce
This is my update method using bunnet update.

    def update(self, entity_id: Any, data: SyncT) -> SyncT:
        """
        Update an entity.

        Args:
            entity_id: The ID of the entity to update
            data: The updated entity data

        Returns:
            The updated entity

        Raises:
            ElementNotFoundException: If no entity with the given ID exists
        """
        # Ensure entity exists
        entity = self.get(entity_id)

        # Update data fields
        update_data = data.model_dump(exclude={"id"}, exclude_unset=True)
        updated_entity = entity.update({"$set": update_data})

        return updated_entity

This is my update method using beanie update

    async def update(self, entity_id: Any, data: AsyncT) -> AsyncT:
        """
        Update an entity.

        Args:
            entity_id: The ID of the entity to update
            data: The updated entity data

        Returns:
            The updated entity

        Raises:
            ElementNotFoundException: If no entity with the given ID exists
        """
        # Ensure entity exists
        entity = await self.get(entity_id)

        # Update data fields
        update_data = data.model_dump(exclude={"id"}, exclude_unset=True)
        updated_entity = await entity.update({"$set": update_data})

        return updated_entity

as you can see they are almost identical. Now I have an entity that has an is_active field, using beanie everything updates normally, but if I try to update the entity using bunnet is_active fields gets ignored unless I specify by_alias=True inside the model_dump.

Expected behavior
I expect both libraries' update method to behave the same.