kubernetes-kcp.tests: fix the eval

Without the change the eval fails as:

    $ nix build --no-link -f. kubernetes-kcp.tests
    error:
       … while evaluating the attribute 'version'
         at pkgs/by-name/ku/kubernetes-kcp/package.nix:52:3:
           51|
           52|   passthru.tests.version = testers.testVersion {
             |   ^
           53|     command = "kcp --version";

       … from call site
         at pkgs/by-name/ku/kubernetes-kcp/package.nix:52:28:
           51|
           52|   passthru.tests.version = testers.testVersion {
             |                            ^
           53|     command = "kcp --version";

       error: function 'testVersion' called without required argument 'package'
       at pkgs/build-support/testers/default.nix:66:5:
           65|   testVersion =
           66|     { package,
             |     ^
           67|       command ? "${package.meta.mainProgram or package.pname or package.name} --version",

pkgs/by-name/ku/kubernetes-kcp/package.nix

@@ -5,6 +5,7 @@
   fetchFromGitHub,
   installShellFiles,
   testers,
+  kubernetes-kcp,
 }:
 
 buildGoModule rec {
@@ -50,6 +51,7 @@ buildGoModule rec {
   '';
 
   passthru.tests.version = testers.testVersion {
+    package = kubernetes-kcp;
     command = "kcp --version";
     # NOTE: Once the go.mod version is pulled in, the version info here needs
     # to be also updated.