Honor SkipIcebergDDLProcessing in PostProcessRenameWritablePgLakeTable

ProcessAlterTable already short-circuits when SkipIcebergDDLProcessing
is set, but rename goes through a different post-process path. Without
this guard, the external-write sync's RENAME COLUMN would trigger a
duplicate metadata write on top of the externally-supplied metadata.

Author: sfc-gh-mslot

pg_lake_table/src/ddl/alter_table.c

@@ -692,6 +692,14 @@ PostProcessRenameWritablePgLakeTable(ProcessUtilityParams * params, void *arg)
 		!(renameStmt->renameType == OBJECT_TABLE ||
 		  renameStmt->renameType == OBJECT_FOREIGN_TABLE))
 	{
+		/*
+		 * When syncing from externally-written Iceberg metadata, the rename
+		 * is already reflected in the new metadata file; skip our own DDL
+		 * tracking and metadata write.
+		 */
+		if (SkipIcebergDDLProcessing)
+			return;
+
 		/* schema has changed, update the metadata */
 		IcebergDDLOperation *ddlOperation = palloc0(sizeof(IcebergDDLOperation));