Docs issue for pd.concat
Hi,

I was recently updating my pandas from 0.24.2 to 1.1.5 and future warning informed me that default value for sort has changed from None to False. It said that to present current behavior I should change it to sort=True. After i updated my package, I checked if sort=None is still accessible and it is, while docs says it accepts only bool.

May I understand that I can still use sort=None to present old behavior? Or should it be depreciated and raise Error?

![image](https://user-images.githubusercontent.com/71095058/118462242-c0f28600-b6fe-11eb-8a7d-dfd45ec40c3c.png)
