Update java example (#5701)

* use the loaded junit version

* add comment

Author: mai93

examples/java/greetings_project/WORKSPACE

@@ -2,8 +2,8 @@ load("@bazel_tools//tools/build_defs/repo:jvm.bzl", "jvm_maven_import_external")
 
 jvm_maven_import_external(
     name = "junit",
-    artifact = "org.junit.jupiter:junit-jupiter-api:5.9.1",
-    artifact_sha256 = "5d2fe4d719dffb25a95d77e9c7a34893cbbb1b4cc6c86f2726af7e0fb7035b2f",
+    artifact = "junit:junit:4.13.2",
+    artifact_sha256 = "8e495b634469d64fb8acfa3495a065cbacc8a0fff55ce1e31007be4c16dc57d3",
     licenses = ["notice"],  # Common Public License 1.0
     server_urls = ["https://repo1.maven.org/maven2"],
 )

examples/java/greetings_project/hello/hello.bazelproject

@@ -18,4 +18,8 @@ additional_languages:
   # dart
   # kotlin
   # python
-  # scala
+  # scala
+
+build_flags:
+  # make sure the junit version loaded in the WORKSPACE is the one used
+  --explicit_java_test_deps