add gc_collects to weakref tests
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 7a2dd0c..3c14c80 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -493,6 +493,7 @@
             e.__context__ = None
             obj = None
             obj = wr()
+            gc_collect()
             self.assertTrue(obj is None, "%s" % obj)
 
         # Some complicated construct
@@ -509,6 +510,7 @@
             except MyException:
                 pass
         obj = None
+        gc_collect()
         obj = wr()
         self.assertTrue(obj is None, "%s" % obj)
 
@@ -523,6 +525,7 @@
         with Context():
             inner_raising_func()
         obj = None
+        gc_collect()
         obj = wr()
         self.assertTrue(obj is None, "%s" % obj)