@anoopshrma please cross-check the link you shared it opening a migration guide at my side.
Anyways if you are using Rasa 3.X please visit this rasa form example repo : https://github.com/RasaHQ/rasa-3.x-form-examples/blob/main/05-validation/actions/actions.py
I hope this will help you, and in FormValidation we use the word Validation after class please ref this: Forms
Demo code:
class ValidateRestaurantForm(FormValidationAction):
def name(self) -> Text:
return "validate_restaurant_form"
OR if I’m missing something do inlighten me, I hope this will help you.