**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
#
#
#
#
import datetime
import itertools
import logging
import multiprocessing
import os
import sched
import signal
import sys
import threading
import time
from collections import defaultdict
from contextlib import redirect_stderr, redirect_stdout, suppress
from datetime import timedelta
from multiprocessing.connection import Connection as MultiprocessingConnection
from typing import Any, Callable, DefaultDict, Dict, Iterable, List, Optional, Set, Tuple
from setproctitle import setproctitle
from sqlalchemy import and_, func, not_, or_, tuple_
from sqlalchemy.exc import OperationalError
from sqlalchemy.orm import load_only, selectinload
from sqlalchemy.orm.session import Session, make_transient
from airflow import models, settings
from airflow.configuration import conf