Fixing test_pickling tests for Python 3.13.

The `Handler.lock` is substituted for a `nullcontext`, keeping Python 3.13 happy. A no-op stub for `Handler.release` is added, keeping all other Python versions happy.

tests/test_pickling.py

@@ -50,20 +50,30 @@ def _stop(self):
         self.stopped = True
 
 
+class MockLock:
+    def __enter__(self):
+        pass
+
+    def __exit__(self, *excinfo):
+        pass
+
+
 class StandardHandler(logging.Handler):
     def __init__(self, level):
         super().__init__(level)
         self.written = ""
-        self.lock = None
 
     def emit(self, record):
         self.written += record.getMessage()
 
     def acquire(self):
         pass
 
+    def release(self):
+        pass
+
     def createLock(self):  # noqa: N802
-        return None
+        self.lock = MockLock()
 
 
 def format_function(record):