sqlsmith: disable NAME type in postgres mode

The NAME type is known to have different behavior in CRDB than in
postgres, in that casting to name truncates a string to 63 characters in
postgres, but not in CRDB, causing sqlsmith test failures. For backwards
compatibility, CRDB behavior is not being changed to match postgres,
at least for now.

The fix it to prevent sqlsmith tests which use postgres mode (which
implies it is comparing CRDB results with postgres) from generating NAME
as a random type for testing.

Fixes: cockroachdb#107895

Release note: None

pkg/internal/sqlsmith/type.go

@@ -105,6 +105,11 @@ func (s *Smither) randType() *types.T {
 			(s.disableOIDs && typ.Family() == types.OidFamily) {
 			continue
 		}
+		if s.postgres && typ == types.Name {
+			// Name type in CRDB doesn't match Postgres behavior. Exclude for tests
+			// which compare CRDB behavior to Postgres.
+			continue
+		}
 		break
 	}
 	return typ