[hotfix][oceanbase] Fix the default string encoding(#1294)

This closes #1294.

flink-connector-oceanbase-cdc/src/main/java/com/ververica/cdc/connectors/oceanbase/source/OceanBaseJdbcConverter.java

@@ -134,7 +134,7 @@ public class OceanBaseJdbcConverter {
             case Types.BINARY:
                 return ByteBuffer.wrap(value.toString().getBytes(StandardCharsets.UTF_8));
             default:
-                return value.toString();
+                return value.toString(StandardCharsets.UTF_8.toString());
         }
     }