openssh: make the NixOS tests for openssh test the actual derivation being built (#450716)

  passthru = {

    inherit withKerberos;

    tests = {

      borgbackup-integration = nixosTests.borgbackup;

      nixosTest = nixosTests.openssh;

      initrd-network-openssh = nixosTests.initrd-network-ssh;

    tests =

      let

        withThisSsh =

          test:

          test.extendNixOS {

            module = {

              services.openssh.package = lib.mkForce finalAttrs.finalPackage;

            };

          };

      in

      {

        borgbackup-integration = withThisSsh nixosTests.borgbackup;

        nixosTest = withThisSsh nixosTests.openssh;

        initrd-network-openssh = withThisSsh nixosTests.initrd-network-ssh;

        openssh = finalAttrs.finalPackage.overrideAttrs (previousAttrs: {

          pname = previousAttrs.pname + "-test";

          doCheck = true;