[appstream] Fix app url

org.kde.Help.appdata.xml

@@ -289,7 +289,7 @@
       <image width="1920" height="1044">https://kde.org/images/screenshots/khelpcenter.png</image>
     </screenshot>
   </screenshots>
-  <url type="homepage">https://www.kde.org/applications/system/khelpcenter</url>
+  <url type="homepage">https://apps.kde.org/help/</url>
   <url type="bugtracker">https://bugs.kde.org/enter_bug.cgi?format=guided&amp;product=khelpcenter</url>
   <url type="donation">https://www.kde.org/community/donations/?app=khelpcenter&amp;source=appdata</url>
   <project_group>KDE</project_group>