manfull.pl: Adjust pattern for current makeinfo

* mk/manfull.pl: During patching of single-page html manuals allow
current form of table of contents headers.

Older makeinfo did not add "contents-heading" class to "<h2>" element.
Helper script failed to properly modify HTML files generated by current
version of makeinfo.  With partially patched file, CSS stiles intended
for table of contents were applied to all unordered lists, so e.g. in
"Plain Lists" section items were bold and with missed markers.

mk/manfull.pl

@@ -13,7 +13,7 @@ while (<IN>) {
   } elsif (/<div class="contents">/) {
     print OUT;
     print OUT '<p>This is the official manual for the latest <a href="https://orgmode.org">Org mode</a> release.</p><div id="table-of-contents">';
-  } elsif (/<h2>Table of Contents<\/h2>/) {
+  } elsif (/<h2>Table of Contents<\/h2>|<h2 class="contents-heading">/) {
     print OUT;
     print OUT '<a href="https://orgmode.org">https://orgmode.org</a><br/><div id="text-table-of-contents">';
     $toc = 1;