fix(nix): use pkgs fetcher

keycloak/default.nix

@@ -7,9 +7,10 @@
 }:
 let
   lescommuns-themes = lib.sources.cleanSourceWith {
-    src = builtins.fetchGit {
+    src = pkgs.fetchgit {
       url = "https://forge.liiib.re/lescommuns/theme-sso.git";
       rev = "6a41ff1ea92d81eb0d6d6bc1bd85f438e035693a";
+      hash = "sha256-Z6tAUrJYIxnGCOhlworMo8rSTVdiIlOxHWW0aLbonVo=";
     };
     filter = path: type: type == "directory";
   };