Bug 27526: Fix perlcritic in tests

Problem while critiquing "t/db_dependent/Koha/Item.t": Can't parse code: Encountered unexpected character '195'

non-ascii chars must be quoted when used as hash keys

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

t/db_dependent/Koha/Item.t

@@ -1137,8 +1137,8 @@ subtest 'columns_to_str' => sub {
     my $s = $item->columns_to_str;
     is( $s->{itemlost}, 'Lost' );
     is( $s->{dateaccessioned}, '2020-12-15');
-    is( $s->{é}, 'value é');
-    is( $s->{è}, $library->branchname );
+    is( $s->{'é'}, 'value é');
+    is( $s->{'è'}, $library->branchname );
 
     $cache->clear_from_cache("MarcStructure-0-");
     $cache->clear_from_cache("MarcStructure-1-");