Fix session test

Author: aclark4life

pymongo/asynchronous/client_session.py

@@ -548,6 +548,7 @@ def _check_ended(self) -> None:
             raise InvalidOperation("Cannot use ended session")
 
     async def __aenter__(self) -> AsyncClientSession:
+        _SESSION.set(self)
         return self
 
     async def __aexit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:

pymongo/synchronous/client_session.py

@@ -547,6 +547,7 @@ def _check_ended(self) -> None:
             raise InvalidOperation("Cannot use ended session")
 
     def __enter__(self) -> ClientSession:
+        _SESSION.set(self)
         return self
 
     def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None: