chore: correct internal link in v31 notes

Updated link in release notes for AppApi app.

Signed-off-by: Josh <josh.t.richards@gmail.com>

Author: joshtrichards

admin_manual/release_notes/upgrade_to_31.rst

@@ -56,7 +56,7 @@ See :doc:`../configuration_files/previews_configuration` for details on how to e
 AppApi (app_app) is now a default app
 -------------------------------------
 
-Starting with Nextcloud 30.0.1, the AppApi app is included and enabled by default. See :doc:`../exapps_management` for details.
+Starting with Nextcloud 30.0.1, the AppApi app is included and enabled by default. See :doc:`../exapps_management/index` for details.
 
 This app can be disabled in the standard manner via the *Apps* menu if you do not expect to use AppApi integrations in the near future.