fix: reset _shared_session_lock in all tests for event loop isolation

Address Greptile P1 review: tests that exercise the closed-session code
path need to reset the module-level lock to avoid RuntimeError on
Python < 3.10 when asyncio.Lock is reused across different event loops.

tests/test_litellm/proxy/test_aiohttp_session_recovery.py

@@ -33,9 +33,13 @@ async def test_add_shared_session_attaches_open_session():
 @pytest.mark.asyncio
 async def test_add_shared_session_recreates_closed_session():
     """When the shared session is closed, it should be recreated."""
+    import litellm.proxy.route_llm_request as route_module
     from litellm.proxy import proxy_server as proxy_server_module
     from litellm.proxy.route_llm_request import add_shared_session_to_data
 
+    # Reset the module-level lock so each test uses the current event loop
+    route_module._shared_session_lock = None
+
     closed_session = MagicMock()
     closed_session.closed = True
 
@@ -64,9 +68,13 @@ async def test_add_shared_session_recreates_closed_session():
 @pytest.mark.asyncio
 async def test_add_shared_session_handles_recreation_failure():
     """When recreation fails, data should not contain shared_session."""
+    import litellm.proxy.route_llm_request as route_module
     from litellm.proxy import proxy_server as proxy_server_module
     from litellm.proxy.route_llm_request import add_shared_session_to_data
 
+    # Reset the module-level lock so each test uses the current event loop
+    route_module._shared_session_lock = None
+
     closed_session = MagicMock()
     closed_session.closed = True