CREATE INDEX: do update index stats if autovacuum=off.

This fixes a thinko from commit d611f8b.  The intent was to prevent
updating the stats of the pre-existing heap if autovacuum is off,
but it also disabled updating the stats of the just-created index.
There is AFAICS no good reason to do the latter, since there could not
be any pre-existing stats to refrain from overwriting, and the zeroed
stats that are there to begin with are very unlikely to be useful.
Moreover, the change broke our cross-version upgrade tests again.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1116282.1741374848@sss.pgh.pa.us

Author: tglsfdc

src/backend/catalog/index.c

@@ -2847,20 +2847,20 @@ index_update_stats(Relation rel,
 	 * statistics, as the table statistics may be restored before the index is
 	 * created, and we want to preserve the restored table statistics.
 	 */
-	if (AutoVacuumingActive())
+	if (rel->rd_rel->relkind == RELKIND_RELATION ||
+		rel->rd_rel->relkind == RELKIND_TOASTVALUE ||
+		rel->rd_rel->relkind == RELKIND_MATVIEW)
 	{
-		if (rel->rd_rel->relkind == RELKIND_RELATION ||
-			rel->rd_rel->relkind == RELKIND_TOASTVALUE ||
-			rel->rd_rel->relkind == RELKIND_MATVIEW)
+		if (AutoVacuumingActive())
 		{
 			StdRdOptions *options = (StdRdOptions *) rel->rd_options;
 
 			if (options != NULL && !options->autovacuum.enabled)
 				update_stats = false;
 		}
+		else
+			update_stats = false;
 	}
-	else
-		update_stats = false;
 
 	/*
 	 * Finish I/O and visibility map buffer locks before