Allow relkind 'I' in type_sanity test.

This is cosmetic at present, since no partitioned indexes have
been created yet at the stage of the regression tests when
type_sanity runs.  But it's confusing that this list of allowed
values doesn't match reality, so fix it.

Noted by Jian He.

Discussion: https://postgr.es/m/CACJufxHhr58q-YoBeqnY5P-u8Xe2X5sMtsr3LYE1nQDwdqjB4w@mail.gmail.com

src/test/regress/expected/type_sanity.out

@@ -500,7 +500,7 @@ ORDER BY 1;
 -- Look for illegal values in pg_class fields
 SELECT c1.oid, c1.relname
 FROM pg_class as c1
-WHERE relkind NOT IN ('r', 'i', 'S', 't', 'v', 'm', 'c', 'f', 'p') OR
+WHERE relkind NOT IN ('r', 'i', 'S', 't', 'v', 'm', 'c', 'f', 'p', 'I') OR
     relpersistence NOT IN ('p', 'u', 't') OR
     relreplident NOT IN ('d', 'n', 'f', 'i');
  oid | relname 

src/test/regress/sql/type_sanity.sql

@@ -360,7 +360,7 @@ ORDER BY 1;
 
 SELECT c1.oid, c1.relname
 FROM pg_class as c1
-WHERE relkind NOT IN ('r', 'i', 'S', 't', 'v', 'm', 'c', 'f', 'p') OR
+WHERE relkind NOT IN ('r', 'i', 'S', 't', 'v', 'm', 'c', 'f', 'p', 'I') OR
     relpersistence NOT IN ('p', 'u', 't') OR
     relreplident NOT IN ('d', 'n', 'f', 'i');