Refs #34233 -- Used @staticmethod with TextChoices._generate_next_value_().

Now that Python 3.10 is the minimum supported version, we can decorate
_generate_next_value_() with @staticmethod. It wasn't possible before
as Python < 3.10 does not support calling static methods direct from
the class body.

https://docs.python.org/3/library/enum.html#enum.Enum._generate_next_value_

django/db/models/enums.py

@@ -98,6 +98,7 @@ class IntegerChoices(int, Choices):
 class TextChoices(str, Choices):
     """Class for creating enumerated string choices."""
 
+    @staticmethod
     def _generate_next_value_(name, start, count, last_values):
         return name