**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 dr.state == State.FAILED
        expected_callback = DagCallbackRequest(
            full_filepath=dr.dag.fileloc,
            dag_id=dr.dag_id,
            is_failure_callback=True,
            execution_date=dr.execution_date,
            msg="timed_out",
        )
        
        scheduler.processor_agent.send_callback_to_execute.assert_called_once_with(expected_callback)
        session.rollback()
        session.close()
    @parameterized.expand([(State.SUCCESS, "success"), (State.FAILED, "task_failure")])
    def test_dagrun_callbacks_are_called(self, state, expected_callback_msg):
        """
        Test if DagRun is successful, and if Success callbacks is defined, it is sent to DagFileProcessor.
        Also test that SLA Callback Function is called.
        """
        dag = DAG(
            dag_id='test_dagrun_callbacks_are_called',
            start_date=DEFAULT_DATE,
            on_success_callback=lambda x: print("success"),
            on_failure_callback=lambda x: print("failed"),
        )
        DummyOperator(task_id='dummy', dag=dag, owner='airflow')
        scheduler = SchedulerJob(subdir=os.devnull)
        scheduler.processor_agent = mock.Mock()
        scheduler.processor_agent.send_callback_to_execute = mock.Mock()
        scheduler._send_sla_callbacks_to_processor = mock.Mock()