chore: add graphql language to fenced code block for syntax highlighting (#5256)

Author: josefaidt

src/pages/cli/migration/lazy-load-custom-selection-set.mdx

@@ -17,7 +17,7 @@ With the latest Amplify library for Swift, developers now have better query cont
 
 Developers using **API (GraphQL)** can control the data returned from their GraphQL service. The request for a particular model can include or exclude connected models. Let’s take a look at the schema with Post and Comment models in the following examples. A comment belongs to a post and a post has many comments.
 
-```
+```graphql
 enum PostStatus {
   ACTIVE
   INACTIVE