🧵 Don't lock around socket close in #disconnect

It should always be safe to call `@sock.close` without external
synchronization.  And synchronizing here with could get stuck
waiting e.g. for a response_handler looping in the receiver thread.

Author: nevans

lib/net/imap.rb

@@ -1151,9 +1151,7 @@ def disconnect
       rescue Exception => e
         @receiver_thread.raise(e)
       end
-      synchronize do
-        @sock.close
-      end
+      @sock.close
       @receiver_thread.join
       raise e if e
     ensure