**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
execution_date=DEFAULT_DATE,
            start_date=DEFAULT_DATE,
            session=session,
        )
        ti1a = dr1.get_task_instance(task_id='dummy', session=session)
        ti1a.state = State.SCHEDULED
        ti1b = dr1.get_task_instance(task_id='dummy_b', session=session)
        ti1b.state = State.SUCCESS
        session.commit()
        ti2 = dr2.get_task_instance(task_id='dummy', session=session)
        ti2.state = State.SCHEDULED
        session.commit()
        ti3 = TaskInstance(dag3.get_task('dummy'), DEFAULT_DATE)
        ti3.state = State.SCHEDULED
        session.merge(ti3)
        session.commit()
        dagbag = DagBag("/dev/null", include_examples=False, read_dags_from_db=False)
        dagbag.bag_dag(dag1, root_dag=dag1)
        dagbag.bag_dag(dag2, root_dag=dag2)
        dagbag.bag_dag(dag3, root_dag=dag3)
        dagbag.sync_to_db(session)
        session.commit()
        scheduler = SchedulerJob(num_runs=0)
        scheduler.dagbag.collect_dags_from_db()
        scheduler._change_state_for_tis_without_dagrun(
            old_states=[State.SCHEDULED, State.QUEUED], new_state=State.NONE, session=session
        )
        ti1a = dr1.get_task_instance(task_id='dummy', session=session)
        ti1a.refresh_from_db(session=session)
        assert ti1a.state == State.SCHEDULED