**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
self.log.info("Starting the scheduler")
        
        pickle_dags = self.do_pickle and self.executor_class not in UNPICKLEABLE_EXECUTORS
        self.log.info("Processing each file at most %s times", self.num_times_parse_dags)
        
        
        async_mode = not self.using_sqlite
        processor_timeout_seconds: int = conf.getint('core', 'dag_file_processor_timeout')
        processor_timeout = timedelta(seconds=processor_timeout_seconds)
        self.processor_agent = DagFileProcessorAgent(
            dag_directory=self.subdir,
            max_runs=self.num_times_parse_dags,
            processor_factory=type(self)._create_dag_file_processor,
            processor_timeout=processor_timeout,