GIT_SILENT Update Appstream for new release

(cherry picked from commit 0ec4f9a9)

org.kde.ktuberling.appdata.xml

@@ -155,9 +155,9 @@
     <value key="KDE::google_play">https://play.google.com/store/apps/details?id=org.kde.ktuberling</value>
   </custom>
   <releases>
+    <release version="21.04.2" date="2021-06-10"/>
     <release version="21.04.1" date="2021-05-13"/>
     <release version="21.04.0" date="2021-04-22"/>
     <release version="20.12.3" date="2021-03-04"/>
-    <release version="20.12.2" date="2021-02-04"/>
   </releases>
 </component>