security: upgrade Apache ZooKeeper to 3.9.4

- Upgrade from 3.9.3 to 3.9.4 (latest stable)
- Ensures all known security vulnerabilities are patched
- Fixes GHSA-g93m-8x6h-g5gv, GHSA-r978-9m6m-6gm6, GHSA-2hmj-97jw-28jh

test/java/spark/pom.xml

@@ -121,7 +121,7 @@
             <dependency>
                 <groupId>org.apache.zookeeper</groupId>
                 <artifactId>zookeeper</artifactId>
-                <version>3.9.3</version>
+                <version>3.9.4</version>
             </dependency>
 
             <!-- Apache Commons - Fix CVEs -->