**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

airflow/jobs/scheduler_job.py
:return: Number of TIs enqueued in this iteration
        :rtype: int
        """
        
        with prohibit_commit(session) as guard:
            if settings.USE_JOB_SCHEDULE:
                self._create_dagruns_for_dags(guard, session)
            dag_runs = self._get_next_dagruns_to_examine(session)
            
            
            
            
            
            
            
            #
            
            
            
            
            
            active_runs_by_dag_id = defaultdict(set)
            query = (
                session.query(
                    TI.dag_id,
                    TI.execution_date,
                )
                .filter(
                    TI.dag_id.in_(list({dag_run.dag_id for dag_run in dag_runs})),
                    TI.state.notin_(list(State.finished) + [State.REMOVED]),