**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
else:
                assert start_date is None
                assert end_date is None
                assert duration is None
@pytest.mark.usefixtures("disable_load_example")
class TestSchedulerJob(unittest.TestCase):
    def setUp(self):
        clear_db_runs()
        clear_db_pools()
        clear_db_dags()
        clear_db_sla_miss()
        clear_db_errors()
        
        
        self.null_exec = MockExecutor()
        self.patcher = patch('airflow.utils.dag_processing.SerializedDagModel.remove_deleted_dags')
        
        self.patcher_dag_code = patch.object(settings, "STORE_DAG_CODE", False)
        self.patcher.start()
        self.patcher_dag_code.start()
    def tearDown(self):
        self.patcher.stop()
        self.patcher_dag_code.stop()
    @classmethod
    def setUpClass(cls):
        
        non_serialized_dagbag = DagBag(read_dags_from_db=False, include_examples=False)
        non_serialized_dagbag.sync_to_db()
        cls.dagbag = DagBag(read_dags_from_db=True)
    def test_is_alive(self):