Always call System.gc() and System.runFinalization() at least once in awaitGC (#8974)

Author: mcculls

utils/test-utils/src/main/java/datadog/trace/test/util/GCUtils.java

@@ -22,6 +22,8 @@ public static void awaitGC(final WeakReference<?> ref) throws InterruptedExcepti
 
   public static void awaitGC(final WeakReference<?> ref, final long duration, final TimeUnit unit)
       throws InterruptedException {
+    System.gc();
+    System.runFinalization();
     final long waitNanos = unit.toNanos(duration);
     final long start = System.nanoTime();
     while (System.nanoTime() - start < waitNanos) {