For xcoms pushed from different tasks, having the same execution_date and in the same Dag, the result of the xcom_pull with key set as None is not deterministic in its order

**Apache Airflow version**: 2.0


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`):

**Environment**:

- **Cloud provider or hardware configuration**:
- **OS** (e.g. from /etc/os-release):
- **Kernel** (e.g. `uname -a`):
- **Install tools**:
- **Others**:

**What happened**:
When tasks in the same dag push Xcoms, the result of the xcom_pull comes in any order. The order is not deterministic.

**What you expected to happen**:

I expected the order to be deterministic.

**How to reproduce it**:

Run the provided example_xcom dag in the repository multiple times


airflow/models/taskinstance.py
first_task_id = first.task_id
        
        
        if all(t.dag_id == dag_id and t.execution_date == execution_date for t in tis):
            return and_(
                TaskInstance.dag_id == dag_id,
                TaskInstance.execution_date == execution_date,
                TaskInstance.task_id.in_(t.task_id for t in tis),
            )
        if all(t.dag_id == dag_id and t.task_id == first_task_id for t in tis):
            return and_(
                TaskInstance.dag_id == dag_id,
                TaskInstance.execution_date.in_(t.execution_date for t in tis),
                TaskInstance.task_id == first_task_id,
            )
        return or_(
            and_(
                TaskInstance.dag_id == ti.dag_id,
                TaskInstance.task_id == ti.task_id,
                TaskInstance.execution_date == ti.execution_date,
            )
            for ti in tis
        )
TaskInstanceStateType = Tuple[TaskInstanceKey, str]
class SimpleTaskInstance:
    """
    Simplified Task Instance.
    Used to send data between processes via Queues.
    """
    def __init__(self, ti: TaskInstance):