**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
assert orm_dag is not None
        scheduler = SchedulerJob(subdir=os.devnull)
        scheduler.processor_agent = mock.MagicMock()
        dag = scheduler.dagbag.get_dag('test_verify_integrity_if_dag_not_changed', session=session)
        scheduler._create_dag_runs([orm_dag], session)
        drs = DagRun.find(dag_id=dag.dag_id, session=session)
        assert len(drs) == 1
        dr = drs[0]
        
        with mock.patch('airflow.jobs.scheduler_job.DagRun.verify_integrity') as mock_verify_integrity:
            scheduled_tis = scheduler._schedule_dag_run(dr, {}, session)
            mock_verify_integrity.assert_not_called()
        session.flush()
        assert scheduled_tis == 1
        tis_count = (
            session.query(func.count(TaskInstance.task_id))
            .filter(
                TaskInstance.dag_id == dr.dag_id,
                TaskInstance.execution_date == dr.execution_date,
                TaskInstance.task_id == dr.dag.tasks[0].task_id,
                TaskInstance.state == State.SCHEDULED,
            )
            .scalar()
        )
        assert tis_count == 1
        latest_dag_version = SerializedDagModel.get_latest_version_hash(dr.dag_id, session=session)
        assert dr.dag_hash == latest_dag_version
        session.rollback()
        session.close()
    def test_verify_integrity_if_dag_changed(self):