Fix harmless regex glitch

The regex included `(:? ... )` instead of `(?: ... )` when intending a
non-capturing group, but this was harmless as (1) the captured group
was ignored anyway and (2) the `:?` construct would helpfully match
nothing. The full group would end up being something like
`(:?dt|dd|/dl)` which is just slightly a superset of the intended
`(?:dt|dd|/dl)` and the capture is ignored anyway, so simplify the
regex.

Author: inexorabletash

tools/lint.mjs

@@ -72,7 +72,7 @@ log('massaging HTML...');
   const re = new RegExp(
     '(<(' + tags.join('|') + ')\\b[^>]*>)' +
       '(.*?)' +
-      '(?=<(:?' + tags.join('|') + '|/(' + containers.join('|') + '))\\b)',
+      '(?=<(' + tags.join('|') + '|/(' + containers.join('|') + '))\\b)',
     'sg');
   file = file.replaceAll(
     re, (_, opener, tag, content) => `${opener}${content}</${tag}>`);