Added Informix equivalent of DuplicateKeyException code

Author: sgflt

spring-jdbc/src/main/java/org/springframework/jdbc/support/SQLStateSQLExceptionTranslator.java

@@ -94,7 +94,8 @@ public class SQLStateSQLExceptionTranslator extends AbstractFallbackSQLException
 			301,   // SAP HANA
 			1062,  // MySQL/MariaDB
 			2601,  // MS SQL Server
-			2627   // MS SQL Server
+			2627,  // MS SQL Server
+			-268   // Informix
 		);