Update test dependencies via gradle

Author: tomstepp

runners/google-cloud-dataflow-java/build.gradle

@@ -129,6 +129,8 @@ dependencies {
   testImplementation library.java.google_cloud_dataflow_java_proto_library_all
   testImplementation library.java.jackson_dataformat_yaml
   testImplementation library.java.mockito_inline
+  testImplementation project(":sdks:java:io:kafka")
+  testImplementation library.java.kafka_clients
   validatesRunner project(path: ":sdks:java:core", configuration: "shadowTest")
   validatesRunner project(path: project.path, configuration: "testRuntimeMigration")
   validatesRunner library.java.hamcrest