Add advent calendar to gallery page.

Author: t-paul

gallery.html

@@ -90,6 +90,7 @@ <h1>#SCADvent</h1>
 			<li><a href="advent-calendar-2022/">2022 Advent Calendar</a></li>
 			<li><a href="advent-calendar-2023/">2023 Advent Calendar</a></li>
 			<li><a href="advent-calendar-2024/">2024 Advent Calendar</a></li>
+			<li><a href="advent-calendar-2025/">2025 Advent Calendar</a></li>
 		</ul>
 	</div>