[FLINK-38244][hotfix] Fix case-insensitive error when adding column After an existed column. (apache#4100)

Author: loserwang1024

flink-cdc-connect/flink-cdc-pipeline-connectors/flink-cdc-pipeline-connector-mysql/src/main/java/org/apache/flink/cdc/connectors/mysql/source/parser/CustomAlterTableParserListener.java

@@ -226,6 +226,9 @@ public void exitAlterByAddColumn(MySqlParser.AlterByAddColumnContext ctx) {
                                                         null))));
                     } else if (ctx.AFTER() != null) {
                         String afterColumn = parser.parseName(ctx.uid(1));
+                        if (isTableIdCaseInsensitive) {
+                            afterColumn = afterColumn.toLowerCase(Locale.ROOT);
+                        }
                         changes.add(
                                 new AddColumnEvent(
                                         currentTable,