**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
"""Last DAG runs"""
        allowed_dag_ids = current_app.appbuilder.sm.get_accessible_dag_ids(g.user)
        
        selected_dag_ids = {unquote(dag_id) for dag_id in request.form.getlist('dag_ids') if dag_id}
        if selected_dag_ids:
            filter_dag_ids = selected_dag_ids.intersection(allowed_dag_ids)
        else:
            filter_dag_ids = allowed_dag_ids
        if not filter_dag_ids:
            return wwwutils.json_response({})
        query = session.query(
            DagRun.dag_id,
            sqla.func.max(DagRun.execution_date).label('execution_date'),
            sqla.func.max(DagRun.start_date).label('start_date'),
        ).group_by(DagRun.dag_id)
        
        query = query.filter(DagRun.dag_id.in_(filter_dag_ids))
        resp = {
            r.dag_id.replace('.', '__dot__'): {
                'dag_id': r.dag_id,
                'execution_date': r.execution_date.isoformat(),
                'start_date': r.start_date.isoformat(),
            }
            for r in query
        }
        return wwwutils.json_response(resp)
    @expose('/code')
    @auth.has_access(