**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
delay: float,
            action: Callable,
            arguments=(),
            kwargs={},
        ):  
            def repeat(*args, **kwargs):
                action(*args, **kwargs)
                
                
                
                timers.enter(delay, 1, repeat, args, kwargs)
            timers.enter(delay, 1, repeat, arguments, kwargs)
        
        self.adopt_or_reset_orphaned_tasks()
        call_regular_interval(
            conf.getfloat('scheduler', 'orphaned_tasks_check_interval', fallback=300.0),
            self.adopt_or_reset_orphaned_tasks,
        )
        call_regular_interval(
            conf.getfloat('scheduler', 'pool_metrics_interval', fallback=5.0),
            self._emit_pool_metrics,
        )
        call_regular_interval(
            conf.getfloat('scheduler', 'clean_tis_without_dagrun_interval', fallback=15.0),
            self._clean_tis_without_dagrun,
        )
        for loop_count in itertools.count(start=1):