aws-cdk-cli.tests: fix the eval

Without the change the eval fails on `master` as:

    $ nix build --no-link -f. aws-cdk-cli.tests
    error:
       … while evaluating the attribute 'version'
         at pkgs/by-name/aw/aws-cdk-cli/package.nix:104:5:
          103|   passthru = {
          104|     tests.version = testers.testVersion { package = finalAttrs.package; };
             |     ^
          105|     updateScript = nix-update-script {

       … while evaluating the 'name' attribute of a derivation

       … while evaluating a branch condition
         at lib/strings.nix:2882:5:
         2881|     # First detect the common case of already valid strings, to speed those up
         2882|     if stringLength string <= 207 && okRegex string != null then
             |     ^
         2883|       unsafeDiscardStringContext string

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'package' missing
       at pkgs/by-name/aw/aws-cdk-cli/package.nix:104:53:
          103|   passthru = {
          104|     tests.version = testers.testVersion { package = finalAttrs.package; };
             |                                                     ^
          105|     updateScript = nix-update-script {