fix IcebergMetadataApplier

Author: ChaomingZhangCN

flink-cdc-connect/flink-cdc-pipeline-connectors/flink-cdc-pipeline-connector-iceberg/src/main/java/org/apache/flink/cdc/connectors/iceberg/sink/IcebergMetadataApplier.java

@@ -124,6 +124,9 @@ public void applySchemaChange(SchemaChangeEvent schemaChangeEvent)
                 },
                 truncateTableEvent -> {
                     throw new UnsupportedSchemaChangeEventException(truncateTableEvent);
+                },
+                alterTableEvent -> {
+                    throw new UnsupportedSchemaChangeEventException(alterTableEvent);
                 });
     }