DOC: Update docstring errors for pandas.DataFrame.mean, pandas.DataFr…
Updates the docstring errors for the methods mentioned above. 
![image](https://github.com/pandas-dev/pandas/assets/144747028/34b36412-d63f-49d3-9c20-1205165c9d95)
![image](https://github.com/pandas-dev/pandas/assets/144747028/927601b7-098c-4ea8-95cc-c28c4d630173)
![image](https://github.com/pandas-dev/pandas/assets/144747028/3acb9d60-b2e8-47e9-8f91-1a3af97184dd)
![image](https://github.com/pandas-dev/pandas/assets/144747028/6731d4a5-e83d-4f1b-a80a-421305c75984)

Thanks for the PR! I am getting different results when running the validation script. All the additions you added are not actually missing (not sure why you're getting these results)

Going to close because the existing errors are actually correct, but it would be really appreciated if you can open a PR to update the docstrings to fix the errors!