Merge pull request #198056 from hercules-ci/nixos-fix-nixpkgs-assertion-when-pkgs-is-set

nixos/modules/misc/nixpkgs.nix

···
             else "nixpkgs.localSystem";
           pkgsSystem = finalPkgs.stdenv.targetPlatform.system;
         in {
-          assertion = !hasPlatform -> nixosExpectedSystem == pkgsSystem;
+          assertion = constructedByMe -> !hasPlatform -> nixosExpectedSystem == pkgsSystem;
           message = "The NixOS nixpkgs.pkgs option was set to a Nixpkgs invocation that compiles to target system ${pkgsSystem} but NixOS was configured for system ${nixosExpectedSystem} via NixOS option ${nixosOption}. The NixOS system settings must match the Nixpkgs target system.";
         }
       )