Update iac-vulnerabilities.md

YAML sample code contained two errors:
1. As mentioned in the Note, categories is case sensitive (Iac => IaC)
2. Used single quotes to start the string and double quotes to end

Author: davidknise

articles/defender-for-cloud/iac-vulnerabilities.md

@@ -30,7 +30,7 @@ Once you have set up the Microsoft Security DevOps GitHub action or Azure DevOps
 
     ```yml
     with:
-        categories: 'Iac"
+        categories: 'IaC'
     ```
 
     > [!NOTE]