Reset the proper GUC in create_index test.

Thinko in commit a4523c5aa.  It doesn't really affect anything at
present, but it would be a problem if any tests added later in this
file ought to get index-only-scan plans.  Back-patch, like the previous
commit, just to avoid surprises in case we add such a test and then
back-patch it.

Nikita Glukhov

Discussion: https://postgr.es/m/8b70135d-ad38-bdd8-ac92-71e2b3c273cf@postgrespro.ru

src/test/regress/expected/create_index.out

@@ -2762,7 +2762,7 @@ ORDER BY thousand;
         1 |     1001
 (2 rows)
 
-RESET enable_indexscan;
+RESET enable_indexonlyscan;
 --
 -- Check elimination of constant-NULL subexpressions
 --

src/test/regress/sql/create_index.sql

@@ -927,7 +927,7 @@ SELECT thousand, tenthous FROM tenk1
 WHERE thousand < 2 AND tenthous IN (1001,3000)
 ORDER BY thousand;
 
-RESET enable_indexscan;
+RESET enable_indexonlyscan;
 
 --
 -- Check elimination of constant-NULL subexpressions