**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
root=root,
        )
    @expose('/graph')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_LOG),
        ]
    )
    @gzipped
    @action_logging
    @provide_session
    def graph(self, session=None):
        """Get DAG as Graph."""
        dag_id = request.args.get('dag_id')
        dag = current_app.dag_bag.get_dag(dag_id)
        if not dag:
            flash(f'DAG "{dag_id}" seems to be missing.', "error")
            return redirect(url_for('Airflow.index'))
        root = request.args.get('root')
        if root:
            dag = dag.partial_subset(task_ids_or_regex=root, include_upstream=True, include_downstream=False)
        arrange = request.args.get('arrange', dag.orientation)
        nodes = task_group_to_dict(dag.task_group)
        edges = dag_edges(dag)
        dt_nr_dr_data = get_date_time_num_runs_dag_runs_form_data(request, session, dag)
        dt_nr_dr_data['arrange'] = arrange
        dttm = dt_nr_dr_data['dttm']
        class GraphForm(DateTimeWithNumRunsWithDagRunsForm):