Update pithos to version 1.6.0 / rev 15 via SR 1040196
    
    https://build.opensuse.org/request/show/1040196
    by user dimstar + dimstar_suse
    - Update to version 1.6.0:
      + This is a fairly small release with some UI tweaks and bug
        fixes:
        - Use a headerbar for main window.
        - Add Ctrl+r shortcut to open stations popover.
        - Remove access to host keyring when in flatpak.
        - notification_icon: Remove dependency on libappindicator.
          StatusNotifier is directly supported but XEmbed trays are no
          longer supported.