Invalid syntax of GDM dconf profile

[jtojnar]

As mentioned in #54150, 1af8f3a broke the syntax of GDM dconf profile.

• https://developer.gnome.org/dconf/unstable/dconf-overview.html#id-1.2.5
• https://gitlab.gnome.org/GNOME/dconf/blob/9c4a4f2baef7c35934a8b05fb61148f0a356940d/engine/dconf-engine-profile.c#L110-138
• https://gitlab.gnome.org/GNOME/dconf/blob/9c4a4f2baef7c35934a8b05fb61148f0a356940d/engine/dconf-engine-source.c#L74-128

nixpkgs/nixos/modules/services/x11/display-managers/gdm.nix

Lines 157 to 160 in cd29409

	programs.dconf.profiles.gdm = pkgs.writeText "dconf-gdm-profile" ''
	system-db:local
	${gdm}/share/dconf/profile/gdm
	'';

Mar 14 01:18:29 nixos .gsd-color-wrap[866]: unknown dconf database description: /nix/store/95j1l8952q7k4k1dpx0ah3rv8vh90csk-gdm-3.30.3/share/dconf/profile/gdm
Mar 14 01:18:29 nixos .gsd-color-wrap[866]: unable to open file '/etc/dconf/db/local': Failed to open file “/etc/dconf/db/local”: open() failed: No such file or directory; expect degraded performance

[jtojnar]

We should probably concatenate our system-db definition with the original profile. And only when we are creating the database.

[worldofpeace]

#63790 fixed this