more robust systemd configuration;

--- a/src/Pure/Tools/phabricator.scala	Tue Jan 23 15:02:52 2024 +0100
+++ b/src/Pure/Tools/phabricator.scala	Tue Jan 23 16:30:29 2024 +0100
@@ -855,7 +855,7 @@
     Linux.service_install(ssh_name,
 """[Unit]
 Description=OpenBSD Secure Shell server for Isabelle/Phabricator
-After=network.target auditd.service
+After=network.target auditd.service isabelle-phabricator-phd.service
 ConditionPathExists=!/etc/ssh/sshd_not_to_be_run
 
 [Service]