PipelineRun.getSteps returns list of Step objects, not StepRun

- **Package Name**: azureml-sdk[notebooks]
- **Package Version**: 1.52.0
- **Operating System**: Ubuntu 20.04.4 LTS
- **Python Version**: 3.9.5

**Describe the bug**
When using function getSteps() of the class azureml.pipeline.core.PipelineRun, the returned object is a list of Step objects, not StepRun objects as described in the documentation.

**To Reproduce**
Steps to reproduce the behavior:
`pipe_run = PipelineRun(experiment=exper, run_id=pipeline_runs[0].get_details()['runId'])
step_run = pipe_run.find_step_run('cold_start_handling_knn_step')[0]
step_run.get_output_data('recommendations_all')`

**Expected behavior**
I expect to get a list of StepRun objects from the function find_step_run, but get a list of Run objects. Therefore, I cannot get the output using the get_outputs or get_output_data functions as those are only available for the StepRun objects.

**Screenshots**

從 Ubuntu 上回報的 azureml-sdk[notebooks] 1.52.0 重現開始，並執行 issue 中的 PipelineRun 和 find_step_run 程式碼片段。將實際回傳的物件型別與文件化 API 進行比對，並確認 get_output_data 是否可用。當文件化的回傳型別與可使用的輸出方法一致時，即表示完成。

由索引模型根據 Issue 內容生成。