Fix UTF-8 mojibake in #!vim highlighted blocks

t/vim_utf8_encoding.t

@@ -0,0 +1,67 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use utf8;
+use charnames qw(:full);
+
+use lib 'lib';
+use lib 'inc/WWW-AdventCalendar/lib';
+
+use DateTime;
+use Test::More;
+use WWW::AdventCalendar::Article;
+
+{
+    no warnings qw(redefine once);
+    *WWW::AdventCalendar::uri = sub { shift->{uri} };
+}
+
+my $calendar = bless { uri => 'https://example.test/' }, 'WWW::AdventCalendar';
+
+my $open_q  = "\N{LEFT-POINTING DOUBLE ANGLE QUOTATION MARK}";
+my $close_q = "\N{RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK}";
+
+my $body = <<"POD";
+=encoding utf8
+
+=begin perl
+
+    ok( headerOK( \$str ), "${open_q}\$str${close_q} is OK" );
+
+=end perl
+
+    #!vim perl
+
+          debug "${open_q}\$firstLine${close_q} is proper markdown ho, ho, ho";
+POD
+
+my $article = WWW::AdventCalendar::Article->new(
+    date     => DateTime->new( year => 2024, month => 12, day => 15 ),
+    author   => 'Test Author <test@example.com>',
+    title    => 'UTF-8 render check',
+    topic    => 'Encoding',
+    body     => $body,
+    calendar => $calendar,
+);
+
+my $html = $article->body_html;
+
+like(
+    $html,
+    qr/\Q$open_q\E\$str\Q$close_q\E is OK/,
+    'begin perl block keeps UTF-8 guillemets',
+);
+
+like(
+    $html,
+    qr/\Q$open_q\E<\/span><span class="synIdentifier">\$firstLine<\/span><span class="synConstant">\Q$close_q\E is proper markdown ho, ho, ho/s,
+    '#!vim perl block keeps UTF-8 guillemets',
+);
+
+unlike(
+    $html,
+    qr/«/,
+    'no double-encoded UTF-8 marker remains',
+);
+
+done_testing;