Be more tolerant of slow GC in the tests.

pyjapc/tests/test_pyjapc.py

@@ -830,7 +830,10 @@ def test_subscription_callback_object_deletion(japc, japc_mock):
     gc.collect()
 
     # Java GC is not instant, so let's give it a chance to finish.
-    time.sleep(0.1)
+    for _ in range(10):
+        if destroyed:
+            break
+        time.sleep(0.1)
 
     assert destroyed