**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
"""Runs Task Instance."""
        dag_id = request.form.get('dag_id')
        task_id = request.form.get('task_id')
        origin = get_safe_url(request.form.get('origin'))
        dag = current_app.dag_bag.get_dag(dag_id)
        task = dag.get_task(task_id)
        execution_date = request.form.get('execution_date')
        execution_date = timezone.parse(execution_date)
        ignore_all_deps = request.form.get('ignore_all_deps') == "true"
        ignore_task_deps = request.form.get('ignore_task_deps') == "true"
        ignore_ti_state = request.form.get('ignore_ti_state') == "true"
        executor = ExecutorLoader.get_default_executor()
        valid_celery_config = False
        valid_kubernetes_config = False
        try:
            from airflow.executors.celery_executor import CeleryExecutor
            valid_celery_config = isinstance(executor, CeleryExecutor)
        except ImportError:
            pass
        try:
            from airflow.executors.kubernetes_executor import KubernetesExecutor
            valid_kubernetes_config = isinstance(executor, KubernetesExecutor)
        except ImportError:
            pass
        if not valid_celery_config and not valid_kubernetes_config:
            flash("Only works with the Celery or Kubernetes executors, sorry", "error")
            return redirect(origin)
        ti = models.TaskInstance(task=task, execution_date=execution_date)
        ti.refresh_from_db()