**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
"""Make sure a task in an orphaned state is not reset if it has no dagrun. """
        dag_id = 'test_reset_orphaned_tasks_nonexistent_dagrun'
        dag = DAG(dag_id=dag_id, start_date=DEFAULT_DATE, schedule_interval='@daily')
        task_id = dag_id + '_task'
        task = DummyOperator(task_id=task_id, dag=dag)
        scheduler = SchedulerJob(subdir=os.devnull)
        session = settings.Session()
        ti = TaskInstance(task=task, execution_date=DEFAULT_DATE)
        session.add(ti)
        session.flush()
        ti.refresh_from_db()
        ti.state = State.SCHEDULED
        session.merge(ti)
        session.flush()
        assert 0 == scheduler.adopt_or_reset_orphaned_tasks(session=session)
        session.rollback()
    def test_reset_orphaned_tasks_no_orphans(self):