nix: use gcc15

Author: FridayFaerie

flake.lock

@@ -18,6 +18,7 @@ in {
     inputs.hyprwayland-scanner.overlays.default
     (final: prev: {
       hyprsunset = prev.callPackage ./default.nix {
+        stdenv = prev.gcc15Stdenv;
         version = version + "+date=" + (mkDate (inputs.self.lastModifiedDate or "19700101")) + "_" + (inputs.self.shortRev or "dirty");
       };
     })