catppuccin-sddm: fix background path substitution

- Upstream changed the `CustomBackground` configuration option to use
  `"backgrounds/wall.png"` instead of `"backgrounds/wall.jpg"`.

- See: https://github.com/catppuccin/sddm/commit/f5418099#diff-e121ebe3

- Resolves: https://github.com/NixOS/nixpkgs/issues/441194

pkgs/by-name/ca/catppuccin-sddm/package.nix

@@ -64,7 +64,7 @@ stdenvNoCC.mkDerivation (finalAttrs: {
 
     ${lib.optionalString (background != null) ''
       substituteInPlace $configFile \
-        --replace-fail 'Background="backgrounds/wall.jpg"' 'Background="${background}"' \
+        --replace-fail 'Background="backgrounds/wall.png"' 'Background="${background}"' \
         --replace-fail 'CustomBackground="false"' 'CustomBackground="true"'
     ''}