Use default connection in _get_connection

[heysaeid]

Today, out of habit and curiosity, I was messing around with the library when the following item caught my attention:
Why can't we use the default connection for _get_connection when we have multiple databases? 🤔

def _get_connection(connection_name: Optional[str]) -> "BaseDBAsyncClient":
    if connection_name:
        connection = connections.get(connection_name)
    elif len(connections.db_config) == 1:
        connection_name = next(iter(connections.db_config.keys()))
        connection = connections.get(connection_name)
    else:
        raise ParamsError(
            "You are running with multiple databases, so you should specify"
            f" connection_name: {list(connections.db_config)}"
        )
    return connection