Fix broken XML formatting in EXPLAIN output for incremental sorts.

The ExplainCloseGroup arguments for incremental sort usage data
didn't match the corresponding ExplainOpenGroup.  This only matters
for XML-format output, which is probably why we'd not noticed.

Daniel Gustafsson, per bug #16683 from Frits Jalvingh

Discussion: https://postgr.es/m/16683-8005033324ad34e9@postgresql.org

src/backend/commands/explain.c

@@ -2827,7 +2827,7 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 			ExplainPropertyInteger("Peak Sort Space Used", "kB",
 								   groupInfo->maxMemorySpaceUsed, es);
 
-			ExplainCloseGroup("Sort Spaces", memoryName.data, true, es);
+			ExplainCloseGroup("Sort Space", memoryName.data, true, es);
 		}
 		if (groupInfo->maxDiskSpaceUsed > 0)
 		{
@@ -2844,7 +2844,7 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 			ExplainPropertyInteger("Peak Sort Space Used", "kB",
 								   groupInfo->maxDiskSpaceUsed, es);
 
-			ExplainCloseGroup("Sort Spaces", diskName.data, true, es);
+			ExplainCloseGroup("Sort Space", diskName.data, true, es);
 		}
 
 		ExplainCloseGroup("Incremental Sort Groups", groupName.data, true, es);