Mark GC-dependent weakref tests as thread-unsafe

Under --parallel-threads a concurrent collection can turn a test's own
gc.collect() into a no-op, leaving its cycles uncollected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ambv

Lib/test/test_frame.py

@@ -309,6 +309,7 @@ def test_weakref_basic(self):
         support.gc_collect()
         self.assertIsNone(ref())
 
+    @support.thread_unsafe("relies on gc.collect() reclaiming its cycles")
     def test_weakref_live_frame(self):
         refs = []
         def func():
@@ -357,6 +358,7 @@ def test_multiple_weakrefs(self):
             self.assertIsNone(ref())
         self.assertEqual({id(r) for r in called}, {id(refs[3]), id(refs[4])})
 
+    @support.thread_unsafe("relies on gc.collect() reclaiming its cycles")
     def test_weak_key_dictionary(self):
         wkd = weakref.WeakKeyDictionary()
         def _fill():
@@ -367,6 +369,7 @@ def _fill():
         support.gc_collect()
         self.assertEqual(len(wkd), 0)
 
+    @support.thread_unsafe("relies on gc.collect() reclaiming its cycles")
     def test_weak_value_dictionary(self):
         wvd = weakref.WeakValueDictionary()
         def _fill():
@@ -377,6 +380,7 @@ def _fill():
         support.gc_collect()
         self.assertEqual(len(wvd), 0)
 
+    @support.thread_unsafe("relies on gc.collect() reclaiming its cycles")
     def test_weakref_traceback_frames(self):
         # Frames that participate in reference cycles are cleaned up
         # by the cyclic garbage collector.