Fix PredicateModifier enum.

Incorrect indentation meant that the `meaning: sssom:NegatedPredicated` would have been interpreted as _another PredicateModifier value_, instead of the meaning of the `Not` value.

Co-authored-by: Emily Hartley <ehartley@c-path.org>

Author: gouttegd

src/sssom_schema/schema/sssom_schema.yaml

@@ -71,8 +71,8 @@ enums:
 
   predicate_modifier_enum:
     permissible_values:
-      meaning: sssom:NegatedPredicate
       Not: Negating the mapping predicate. The meaning of the triple becomes subject_id is not a predicate_id match to object_id.
+        meaning: sssom:NegatedPredicate
   mapping_cardinality_enum:
     permissible_values:
       "1:1": One-to-one mapping