8258293: tools/jpackage/share/RuntimePackageTest.java#id0 with RuntimePackageTest.testUsrInstallDir2

Reviewed-by: almatvee, herrick
diff --git a/test/jdk/tools/jpackage/share/RuntimePackageTest.java b/test/jdk/tools/jpackage/share/RuntimePackageTest.java
index 9c4c24e..9f7f61e 100644
--- a/test/jdk/tools/jpackage/share/RuntimePackageTest.java
+++ b/test/jdk/tools/jpackage/share/RuntimePackageTest.java
@@ -126,7 +126,11 @@
 
     private static Set<Path> listFiles(Path root) throws IOException {
         try (var files = Files.walk(root)) {
-            return files.map(root::relativize).collect(Collectors.toSet());
+            // Ignore files created by system prefs if any.
+            final Path prefsDir = Path.of(".systemPrefs");
+            return files.map(root::relativize)
+                    .filter(x -> !x.startsWith(prefsDir))
+                    .collect(Collectors.toSet());
         }
     }