[SPARK-39331][PYTHON][TESTS][SS] Check None for offsets in SourceProgress
[SPARK-39331][PYTHON][TESTS][SS] Check None for offsets in SourceProgress

### What changes were proposed in this pull request?

This PR fixes the flaky test (https://github.com/apache/spark/runs/6643112037):

```
Traceback (most recent call last):
  File "/__w/spark/spark/python/pyspark/sql/tests/test_streaming_listener.py", line 121, in test_listener_events
    self.check_progress_event(progress_event)
  File "/__w/spark/spark/python/pyspark/sql/tests/test_streaming_listener.py", line 140, in check_progress_event
    self.check_streaming_query_progress(event.progress)
  File "/__w/spark/spark/python/pyspark/sql/tests/test_streaming_listener.py", line 198, in check_streaming_query_progress
    self.check_source_progress(so)
  File "/__w/spark/spark/python/pyspark/sql/tests/test_streaming_listener.py", line 248, in check_source_progress
    self.assertTrue(isinstance(progress.startOffset, str))
AssertionError: False is not true
```

`startOffset`, `endOffset` and `latestOffset` can be `None`, and this PR changes the possible types in the tests.

### Why are the changes needed?

To fix the flakiness.

### Does this PR introduce _any_ user-facing change?

No, dev-only.

### How was this patch tested?

This PR fixes the test. We should monitor if it fixes the flakiness after it gets merged.

Closes #36718 from HyukjinKwon/SPARK-39331.

Authored-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
Signed-off-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>

zero323/spark,srowen/spark,mahak/spark,WeichenXu123/spark,apache/spark,rednaxelafx/apache-spark,ueshin/apache-spark,wangyum/spark,nchammas/spark,mahak/spark,mahak/spark,rednaxelafx/apache-spark,WeichenXu123/spark,shaneknapp/spark,srowen/spark,srowen/spark,witgo/spark,gengliangwang/spark,gengliangwang/spark,srowen/spark,wangyum/spark,nchammas/spark,dongjoon-hyun/spark,gengliangwang/spark,HyukjinKwon/spark,zzcclp/spark,wangyum/spark,rednaxelafx/apache-spark,zero323/spark,apache/spark,nchammas/spark,witgo/spark,rednaxelafx/apache-spark,shaneknapp/spark,dongjoon-hyun/spark,vinodkc/spark,shaneknapp/spark,hvanhovell/spark,srowen/spark,dongjoon-hyun/spark,wangyum/spark,hvanhovell/spark,JoshRosen/spark,dongjoon-hyun/spark,wangyum/spark,ueshin/apache-spark,rednaxelafx/apache-spark,dongjoon-hyun/spark,wangyum/spark,gengliangwang/spark,vinodkc/spark,HyukjinKwon/spark,wangyum/spark,cloud-fan/spark,WeichenXu123/spark,zzcclp/spark,holdenk/spark,nchammas/spark,zzcclp/spark,ueshin/apache-spark,WeichenXu123/spark,nchammas/spark,gengliangwang/spark,witgo/spark,WeichenXu123/spark,ueshin/apache-spark,apache/spark,apache/spark,ueshin/apache-spark,zero323/spark,nchammas/spark,hvanhovell/spark,ueshin/apache-spark,vinodkc/spark,JoshRosen/spark,hvanhovell/spark,HyukjinKwon/spark,zero323/spark,JoshRosen/spark,srowen/spark,zzcclp/spark,witgo/spark,holdenk/spark,cloud-fan/spark,JoshRosen/spark,gengliangwang/spark,HyukjinKwon/spark,cloud-fan/spark,JoshRosen/spark,cloud-fan/spark,mahak/spark,shaneknapp/spark,holdenk/spark,holdenk/spark,cloud-fan/spark,vinodkc/spark,mahak/spark,HyukjinKwon/spark,srowen/spark,dongjoon-hyun/spark,gengliangwang/spark,witgo/spark,zero323/spark,hvanhovell/spark,shaneknapp/spark,rednaxelafx/apache-spark,vinodkc/spark,JoshRosen/spark,HyukjinKwon/spark,zzcclp/spark,hvanhovell/spark,vinodkc/spark,rednaxelafx/apache-spark,zzcclp/spark,shaneknapp/spark,zzcclp/spark,hvanhovell/spark,holdenk/spark,witgo/spark,shaneknapp/spark,witgo/spark,holdenk/spark,dongjoon-hyun/spark,ueshin/apache-spark,cloud-fan/spark,mahak/spark,apache/spark,apache/spark,zero323/spark,JoshRosen/spark,vinodkc/spark,mahak/spark,WeichenXu123/spark,apache/spark,WeichenXu123/spark,zero323/spark,nchammas/spark,holdenk/spark,cloud-fan/spark,HyukjinKwon/spark