**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
"""
        Bulk update the next_dagrun and next_dagrun_create_after for all the dags.
        We batch the select queries to get info about all the dags at once
        """
        
        
        active_runs_of_dags = dict(
            session.query(DagRun.dag_id, func.count('*'))
            .filter(
                DagRun.dag_id.in_([o.dag_id for o in dag_models]),
                DagRun.state == State.RUNNING,  
                DagRun.external_trigger.is_(False),
            )
            .group_by(DagRun.dag_id)
            .all()
        )
        for dag_model in dag_models:
            
            
            try:
                dag = self.dagbag.get_dag(dag_model.dag_id, session=session)
            except SerializedDagNotFound:
                self.log.exception("DAG '%s' not found in serialized_dag table", dag_model.dag_id)