Use the right interpreter for encoding test.

src/pl/plperl/expected/plperl.out

@@ -656,7 +656,7 @@ CONTEXT:  PL/Perl anonymous code block
 --
 CREATE OR REPLACE FUNCTION perl_zerob() RETURNS TEXT AS $$
   return "abcd\0efg";
-$$ LANGUAGE plperlu;
+$$ LANGUAGE plperl;
 SELECT perl_zerob();
 ERROR:  invalid byte sequence for encoding "UTF8": 0x00
 CONTEXT:  PL/Perl function "perl_zerob"

src/pl/plperl/sql/plperl.sql

@@ -429,7 +429,7 @@ DO $do$ use warnings FATAL => qw(void) ; my @y; my $x = sort @y; 1; $do$ LANGUAG
 --
 CREATE OR REPLACE FUNCTION perl_zerob() RETURNS TEXT AS $$
   return "abcd\0efg";
-$$ LANGUAGE plperlu;
+$$ LANGUAGE plperl;
 SELECT perl_zerob();
 
 -- make sure functions marked as VOID without an explicit return work