Fix: Changelog is Markdown now (take 5465) (#347)

Author: michicc

_posts/2025-04-13-openttd-15-0-beta2.md

@@ -23,5 +23,5 @@ As this beta is the first release featuring badge support, there aren't many upd
 Finally, the usual titlegame competition has been [announced on the forums](https://www.tt-forums.net/viewtopic.php?t=92166).
 
 * [Download](https://www.openttd.org/downloads/openttd-releases/testing.html)
-* [Changelog](https://cdn.openttd.org/openttd-releases/15.0-beta2/changelog.txt)
+* [Changelog](https://cdn.openttd.org/openttd-releases/15.0-beta2/changelog.md)
 * [Bug tracker](https://github.com/OpenTTD/OpenTTD/issues)