home: persist gPodder downloads

i checked `gpo set`: there doesn't appear to be a way to configure the
Downloads dir, so just let gpodder use its preferred dir.

modules/universal/env/home-packages.nix

@@ -67,7 +67,7 @@ let
     gnome-podcasts
     gnome.gnome-system-monitor
     gnome.gnome-terminal  # works on phosh
-    gpodder-configured
+    { pkg = gpodder-configured; dir = "gPodder/Downloads"; }
     gthumb
     inkscape
     krita