Update document return fees

https://gov-uk.atlassian.net/jira/software/c/projects/BT/boards/235?selectedIssue=BT-3000

Updating the minimum and maximum fees for document returns.

The minimum amount has increased from £5 to £5.50.

The maximum amount has increased from £25 to £29.50.

Author: hannahwhittaker

config/smart_answers/rates/register_a_death.yml

@@ -7,5 +7,5 @@
   end_date: 2999-01-01
   register_a_death: 150.00
   copy_of_death_registration_certificate: 50.00
-  minimum_return_fee: 5.00
-  maximum_return_fee: 25.00
+  minimum_return_fee: 5.50
+  maximum_return_fee: 29.50