test: exclude UnsafeNativeLong for duplicate class (#5160)

GWT classes are excluded. Guava-GWT is added because we start
using guava-bom. However GWT (the technology that works on browser)
is not intended to communicate with Google Cloud through Cloud
Java client library.

Author: suztomo

tests/src/test/java/com/google/cloud/BomContentTest.java

@@ -138,10 +138,14 @@ private static void assertUniqueClasses(List<Artifact> allArtifacts)
       for (String className : classPathEntry.getFileNames()) {
         if (className.contains("javax.annotation")
             || className.contains("$")
+            || className.endsWith("package-info")
             || className.equals("com.google.cloud.location.LocationsGrpc")
-            || className.endsWith("package-info")) {
+            || className.equals("com.google.gwt.core.client.UnsafeNativeLong")
+            ) {
           // Ignore annotations, nested classes, and package-info files.
           // Ignore LocationsGrpc classes which are duplicated in generated grpc libraries.
+          // Ignore GWT's UnsafeNativeLong, which appear in om.google.gwt:gwt-dev:2.9.0 and
+          // com.google.jsinterop:base:1.0.0.
           continue;
         }