Refs #26104 -- Replaced unnecessary force_str() with force_text().

django/forms/fields.py

@@ -488,7 +488,7 @@ class DurationField(Field):
             return None
         if isinstance(value, datetime.timedelta):
             return value
-        value = parse_duration(force_str(value))
+        value = parse_duration(force_text(value))
         if value is None:
             raise ValidationError(self.error_messages['invalid'], code='invalid')
         return value