**Apache Airflow version**: 2.0.0


**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**:

I have the following DAG:

```py
from datetime import datetime, timedelta

from airflow import DAG
from airflow.operators.bash_operator import BashOperator

with DAG(
    dag_id="sla_trigger",
    schedule_interval="* * * * *",
    start_date=datetime(2020, 2, 3),
) as dag:
    BashOperator(
        task_id="bash_task",
        bash_command="sleep 30",
        sla=timedelta(seconds=2),
    )

```

And in my understanding this dag should result in SLA miss every time it is triggered (every minute). However, after few minutes of running I don't see any SLA misses...

**What you expected to happen**:

I expect to see SLA if task takes longer than expected.

**How to reproduce it**:

Use the dag from above.

**Anything else we need to know**:

N/A

tests/jobs/test_scheduler_job.py
ti1b = dr1.get_task_instance(task_id='dummy_b', session=session)
        ti1b.refresh_from_db(session=session)
        assert ti1b.state == State.SUCCESS
        ti2 = dr2.get_task_instance(task_id='dummy', session=session)
        ti2.refresh_from_db(session=session)
        assert ti2.state == State.SCHEDULED
        ti3.refresh_from_db(session=session)
        assert ti3.state == State.NONE
        assert ti3.start_date is not None
        assert ti3.end_date is None
        assert ti3.duration is None
        dr1.refresh_from_db(session=session)
        dr1.state = State.FAILED
        
        session.merge(dr1)
        session.commit()
        scheduler._change_state_for_tis_without_dagrun(
            old_states=[State.SCHEDULED, State.QUEUED], new_state=State.NONE, session=session
        )
        
        session.expunge_all()
        ti1a.refresh_from_db(session=session)
        assert ti1a.state == State.NONE
        
        ti1b.refresh_from_db(session=session)
        assert ti1b.state == State.SUCCESS
        
        ti2.refresh_from_db(session=session)
        assert ti2.state == State.SCHEDULED
    def test_change_state_for_tasks_failed_to_execute(self):