Convert override syntax to new version

For details see:
https://docs.yoctoproject.org/next/migration-guides/migration-3.4.html

Note that due to this change the latest point release of Dunfell is
the minimal requirement to be compatible with this layer.

classes/cmake_kdeapp.bbclass

@@ -22,7 +22,7 @@ do_configure_prepend() {
     export XDG_DATA_DIRS=${STAGING_DATADIR}:$XDG_DATA_DIRS
 }
 
-FILES_${PN} += " \
+FILES:${PN} += " \
     ${libdir}/libkdeinit5_*.so \
     ${libdir}/kconf_update_bin/* \
     ${libdir}/plugins/*.so \
@@ -46,7 +46,7 @@ FILES_${PN} += " \
     ${datadir}/qlogging-categories5 \
 "
 
-FILES_${PN}-dev += " \
+FILES:${PN}-dev += " \
     ${datadir}/dbus-1/interfaces/*.xml \
     ${datadir}/kdevappwizard/templates/*.tar.bz2 \
     ${libdir}/cmake/*/*.cmake \