Teach add_json() that jsonb is of TYPCATEGORY_JSON.

This code really needs to be refactored so that there aren't so many copies
that can diverge.  Not to mention that this whole approach is probably
wrong.  But for the moment I'll just stick my finger in the dike.
Per report from Michael Paquier.

src/backend/utils/adt/json.c

@@ -1562,7 +1562,7 @@ add_json(Datum val, bool is_null, StringInfo result, Oid val_type, bool key_scal
 		tcategory = TYPCATEGORY_ARRAY;
 	else if (val_type == RECORDOID)
 		tcategory = TYPCATEGORY_COMPOSITE;
-	else if (val_type == JSONOID)
+	else if (val_type == JSONOID || val_type == JSONBOID)
 		tcategory = TYPCATEGORY_JSON;
 	else
 		tcategory = TypeCategory(val_type);