Allow outcome_table to be set to nil to hide values from outcome tables

Heb ook de ruby-version op 2.7.2 gezet aangezien dat de nieuwe default is geloof ik

https://gitlab.roqua.nl/roqua/roqua/-/issues/6488

lib/quby/compiler/entities/subscore_schema.rb

@@ -16,7 +16,8 @@ module Quby
         attribute :calculation_key?, Types::Symbol
         # [Optional argument] The name of the outcome table where this subscore should be shown. Used for cases where scores
         # differ in subscores too much to be shown as one table. By default, all scores end up in the `:main` table.
-        attribute :outcome_table, Types::Symbol.default(:main).meta(omittable: true)
+        # When outcome_table is explicitly nil, the value should not be shown in outcome tables
+        attribute :outcome_table, Types::Symbol.optional.default(:main)
       end
     end
   end