Bugfix: resources in `executor_config` breaks Graph View in UI (#15199)

closes https://github.com/apache/airflow/issues/14327

When using `KubernetesExecutor` and the task as follows:

```python
PythonOperator(
    task_id=f"sync_{table_name}",
    python_callable=sync_table,
    provide_context=True,
    op_kwargs={"table_name": table_name},
    executor_config={"KubernetesExecutor": {"request_cpu": "1"}},
    retries=5,
    dag=dag,
)
```

it breaks the UI as settings resources in such a way is only there
for backwards compatibility.

This commits fixes it.

(cherry picked from commit 7b577c35e2)

airflow/utils/json.py

@@ -66,7 +66,7 @@ class AirflowJsonEncoder(JSONEncoder):
             obj, (np.float_, np.float16, np.float32, np.float64, np.complex_, np.complex64, np.complex128)
         ):
             return float(obj)
-        elif k8s is not None and isinstance(obj, k8s.V1Pod):
+        elif k8s is not None and isinstance(obj, (k8s.V1Pod, k8s.V1ResourceRequirements)):
             from airflow.kubernetes.pod_generator import PodGenerator
 
             return PodGenerator.serialize_pod(obj)