fix: md format

Author: MarkoMin

spec/Section 5 -- Validation.md

@@ -726,8 +726,8 @@ fragment conflictingDifferingResponses on Pet {
 
 **Explanatory Text**
 
-:: A field subselection is not allowed on leaf fields. A _leaf field_ is any field
-with a scalar or enum unwrapped type.
+:: A field subselection is not allowed on leaf fields. A _leaf field_ is any
+field with a scalar or enum unwrapped type.
 
 The following is valid.