**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

tests/serialization/test_dag_serialization.py
import unittest
from datetime import datetime, timedelta, timezone
from glob import glob
from unittest import mock
import pytest
from dateutil.relativedelta import FR, relativedelta
from kubernetes.client import models as k8s
from parameterized import parameterized
from airflow.hooks.base import BaseHook
from airflow.kubernetes.pod_generator import PodGenerator
from airflow.models import DAG, Connection, DagBag, TaskInstance
from airflow.models.baseoperator import BaseOperator, BaseOperatorLink
from airflow.operators.bash import BashOperator
from airflow.security import permissions
from airflow.serialization.json_schema import load_dag_schema_dict
from airflow.serialization.serialized_objects import SerializedBaseOperator, SerializedDAG
from tests.test_utils.mock_operators import CustomOperator, CustomOpLink, GoogleLink
executor_config_pod = k8s.V1Pod(
    metadata=k8s.V1ObjectMeta(name="my-name"),
    spec=k8s.V1PodSpec(
        containers=[
            k8s.V1Container(name="base", volume_mounts=[k8s.V1VolumeMount(name="my-vol", mount_path="/vol/")])
        ]
    ),
)
serialized_simple_dag_ground_truth = {
    "__version": 1,
    "dag": {
        "default_args": {
            "__type": "dict",