user.list: reserve net/yggdrasil-go user, recycle _nginx from 2012

yggdrasil can drop from root to an unprivileged user, so I'd like to do that in our port.

For that I'd like to recycle the oldest commented-out ID we have.

Feedback? OK?

Index: user.list
===================================================================
RCS file: /cvs/ports/infrastructure/db/user.list,v
diff -u -p -r1.450 user.list
--- user.list 28 Aug 2024 23:11:36 -0000 1.450
+++ user.list 2 Nov 2024 12:56:47 -0000
@@ -101,7 +101,7 @@ id user group port
590 _smsd _smsd comms/smstools
591 _bacula _bacula sysutils/bacula
592 _imapproxy _imapproxy mail/imapproxy
-#593 _nginx _nginx www/nginx
+593 _yggdrasil _yggdrasil net/yggdrasil-go
#594 _ejabberd _ejabberd net/ejabberd
595 _poppassd _poppassd sysutils/openpoppassd
#596 _heartbeat _heartbeat sysutils/heartbeat