fix: switch to nix 2.26 so we can update to 25.05 without issues

configuration.nix

@@ -84,6 +84,8 @@ in
   services.do-agent.enable =
     if config.selfprivacy.server.provider == "DIGITALOCEAN" then true else false;
 
+  nix.package = pkgs.selfprivacy_nix_2_26;
+
   boot.tmp.cleanOnBoot = true;
   networking = {
     hostName = config.selfprivacy.hostname;

flake.nix

@@ -41,6 +41,7 @@
                         kanidm
                         kanidm-provision
                         ;
+                      selfprivacy_nix_2_26 = nixos-unstable.legacyPackages.${prev.system}.nixVersions.nix_2_26;
                     })
                   ];
                   disabledModules = [ "services/security/kanidm.nix" ];