cubicweb #2004658 Issue a warning instead of an exception when closing a closed session [in-progress]

Closing a closed session does not seems that harmful and does not deserve an exception.

However it's suspicious and and warning is appropriate.

Closing a closed session might happen when try: catch or context manager are trying to ensure a session is closed

done in<not specified>
closed by<not specified>
patchOnly emit a warning when repo try to close an already closed session. [rejected]