Update reference/tax_classes.v3.yaml

Co-authored-by: Brett Daniels <theromulans@gmail.com>

Author: bc-vincent-zhao

reference/tax_classes.v3.yaml

@@ -179,7 +179,7 @@ paths:
         '204':
           description: All listed classes deleted successfully.
         '400':
-          description: Delete failed (e.g. class not found).
+          description: Delete failed (e.g., class not found).
           content:
             application/problem+json:
               schema: