[GR-39149] make reference cleaner part of our thread group to give it longer to shut down

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/hpy/GraalHPyContext.java

@@ -2590,7 +2590,7 @@ private ReferenceQueue<Object> createReferenceQueue() {
         // lazily register the runnable that concurrently collects the queued references
         Env env = getContext().getEnv();
         if (env.isCreateThreadAllowed()) {
-            Thread thread = env.createThread(new GraalHPyReferenceCleanerRunnable(referenceQueue), null);
+            Thread thread = env.createThread(new GraalHPyReferenceCleanerRunnable(referenceQueue), null, getContext().getThreadGroup());
             // Make the cleaner thread a daemon; it should not prevent JVM shutdown.
             thread.setDaemon(true);
             thread.start();