application: Integrate with Night Light

This is mostly a nice touch of integration for when
using the Night Light feature. It can be disabled by
switching the 'follow-night-light' dconf key to false,
but no user interface widgetry was added.

build-aux/flatpak/org.gnome.Calendar.json

@@ -22,6 +22,7 @@
         "--talk-name=org.gnome.evolution.dataserver.Calendar7",
         "--talk-name=org.gnome.evolution.dataserver.Sources5",
         "--talk-name=org.gnome.evolution.dataserver.Subprocess.Backend.*",
+        "--talk-name=org.gnome.SettingsDaemon.Color",
         "--filesystem=home",
         "--filesystem=xdg-run/dconf",
         "--filesystem=~/.config/dconf:ro",