**Apache Airflow version**: 2.1.1

**What happened**:

The rendered templates screen doesn't show the operator arguments for TaskFlow API operators.
![image](https://user-images.githubusercontent.com/72943478/125486179-f6dde0be-9f60-4aca-831a-5cfd16e7f006.png)

**What you expected to happen**:

Should show the arguments after any templates have been rendered.

**How to reproduce it**:

Will happen for any `@task` decorated operator.

**Anything else we need to know**:

This issue appears on a number of operators.  Possible solution is to modify the "get_python_source" in utils/code_utils.py to handle list and dict. This would cause any operator that using py as the renderer to handle lists and dicts.  Possibly something like:
```
    if isinstance(x, list):
        return [str(v) for v in x]

    if isinstance(x, dict):
        return {k: str(v) for k, v in x.items()}
```
The converting values to strings seems necessary in order to avoid errors when this is passed to the pygments lexer.
![image](https://user-images.githubusercontent.com/72943478/125494716-01cf0c11-9e5f-45fa-afe2-4f99409edefc.png)

airflow/www/views.py
"""Refresh DAG."""
        dag_id = request.values.get('dag_id')
        orm_dag = session.query(DagModel).filter(DagModel.dag_id == dag_id).first()
        if orm_dag:
            orm_dag.last_expired = timezone.utcnow()
            session.merge(orm_dag)
        session.commit()
        dag = current_app.dag_bag.get_dag(dag_id)
        
        current_app.appbuilder.sm.sync_perm_for_dag(dag_id, dag.access_control)
        flash(f"DAG [{dag_id}] is now fresh as a daisy")
        return redirect(request.referrer)
    @expose('/refresh_all', methods=['POST'])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
        ]
    )
    @action_logging
    def refresh_all(self):
        """Refresh everything"""
        current_app.dag_bag.collect_dags_from_db()
        
        for dag_id, dag in current_app.dag_bag.dags.items():
            current_app.appbuilder.sm.sync_perm_for_dag(dag_id, dag.access_control)
        flash("All DAGs are now up to date")
        return redirect(url_for('Airflow.index'))
    @expose('/gantt')
    @auth.has_access(
        [