apacheKafka.tests: fix the eval

Without the change the eval fails as:

    $ nix build --no-link -f. apacheKafka.tests
    error:
       … while evaluating the attribute 'nixos'
         at pkgs/servers/apache-kafka/default.nix:94:9:
           93|         inherit (versionInfo) jre; # Used by the NixOS module to select the supported JRE
           94|         tests.nixos = versionInfo.nixosTest;
             |         ^
           95|       };

       … while evaluating the attribute 'nixosTest'
         at pkgs/servers/apache-kafka/default.nix:22:7:
           21|       jre = jdk17_headless;
           22|       nixosTest = nixosTests.kafka.kafka_4_0;
             |       ^
           23|     };

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

       error: attribute 'kafka_4_0' missing
       at pkgs/servers/apache-kafka/default.nix:22:19:
           21|       jre = jdk17_headless;
           22|       nixosTest = nixosTests.kafka.kafka_4_0;
             |                   ^
           23|     };

0 files changed, 0 insertions, 0 deletions