appendix/changelog: Update changelog for 2.6 branch

Author: mixxxbot

source/chapters/appendix/changelog.rst

@@ -2837,7 +2837,7 @@ Known issues
 Older Changelog
 ---------------
 
-Find older changelog entries `here <https://github.com/mixxxdj/mixxx/blob/2.5.0/CHANGELOG.md>`__.
+Find older changelog entries in the `2.5.0 Changelog <https://github.com/mixxxdj/mixxx/blob/2.5.0/CHANGELOG.md>`_.
 
 
 .. seealso:: For an overview of previous versions, `take a look