server/process: Disable gc around critical section
    
    The python gc can trigger whilst we're holding the event stream lock
    and when cleaning up objects, they can trigger warnings. This translates
    into a new event which would then need the lock and we can deadlock.
    
    Disable gc whilst we hold that lock to avoid this unfortunate and
    problematic situation.
    
    Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>