Fix year in URL to previous version in changelog (#4375)

@iadawn spotted this mistake in the URL intended to point to the
soon-to-be-previous publication of WCAG 2.1, which went unnoticed in
review of #4179.

Author: kfranqueiro

guidelines/index.html

@@ -728,7 +728,7 @@ <h1>Glossary</h1>
     		<h2>Change Log</h2>
     		<p>This section shows changes for WCAG 2.1 since its publication as a W3C Recommendation. These changes are also recorded as <a href="https://www.w3.org/WAI/WCAG21/errata/">errata</a>.</p>
 
-        <p>Changes since the <a href="https://www.w3.org/TR/2023/REC-WCAG21-20241212/">W3C Recommendation of 12 December 2024</a>:</p>
+        <p>Changes since the <a href="https://www.w3.org/TR/2024/REC-WCAG21-20241212/">W3C Recommendation of 12 December 2024</a>:</p>
         <ul>
           <li>
             Updated content to fully reflect the changes listed under "Changes since the W3C Recommendation of 21 September 2023";