fix(plugin.py): Clear all references for a queue using gc.get_referre…

…rs, similar to the issue described at https://bugs.python.org/issue33081

pytest-embedded/pytest_embedded/plugin.py

@@ -2,6 +2,7 @@
 import datetime
 import dbm
 import functools
+import gc
 import importlib
 import io
 import logging
@@ -409,6 +410,17 @@ def _close_or_terminate(obj):
                 return
 
             try:
+                referrers = gc.get_referrers(obj)
+                for _referrer in referrers:
+                    if isinstance(_referrer, list):
+                        for _i, val in enumerate(_referrer):
+                            if val is obj:
+                                _referrer[_i] = None
+                    elif isinstance(_referrer, dict):
+                        for key, value in _referrer.items():
+                            if value is obj:
+                                _referrer[key] = None
+
                 if isinstance(obj, (subprocess.Popen, multiprocessing.process.BaseProcess)):
                     obj.terminate()
                     obj.kill()