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| };

pkgs/servers/apache-kafka/default.nix

···
       scalaVersion = "2.13";
       sha256 = "sha256-e4Uuk4vAneEM2W7KN1UljH0l+4nb3XYwVxdgfhg14qo=";
       jre = jdk17_headless;
-      nixosTest = nixosTests.kafka.kafka_4_0;
+      nixosTest = nixosTests.kafka.base.kafka_4_0;
     };
     "3_9" = {
       kafkaVersion = "3.9.0";
       scalaVersion = "2.13";
       sha256 = "sha256-q8REAt3xA+OPGbDktE5l2pqDG6nlj9dyUEGxqhaO6NE=";
       jre = jdk17_headless;
-      nixosTest = nixosTests.kafka.kafka_3_9;
+      nixosTest = nixosTests.kafka.base.kafka_3_9;
     };
     "3_8" = {
       kafkaVersion = "3.8.1";
       scalaVersion = "2.13";
       sha256 = "sha256-IhdChtYMqmKyVQbEhpRLxuBNjLLS8VCD0v60gjl3i2I=";
       jre = jdk17_headless;
-      nixosTest = nixosTests.kafka.kafka_3_8;
+      nixosTest = nixosTests.kafka.base.kafka_3_8;
     };
     "3_7" = {
       kafkaVersion = "3.7.1";
       scalaVersion = "2.13";
       sha256 = "sha256-YqyuShQ92YPcfrSATVdEugxQsZm1CPWZ7wAQIOJVj8k=";
       jre = jdk17_headless;
-      nixosTest = nixosTests.kafka.kafka_3_7;
+      nixosTest = nixosTests.kafka.base.kafka_3_7;
     };
   };