swarm-logs-auth: PrivateTmp=disconnected, as DynamicUser implied

DynamicUser implies PrivateTmp=disconnected (systemd.exec(5)), a tmpfs
of the unit's own rather than a private directory reachable from the
host namespace. The explicit setting now matches what the unit ran
with before it moved to a static user.

Refs #5235

nix/host-modules/swarm-victorialogs.nix

@@ -414,7 +414,7 @@ in
         SyslogIdentifier = logsAuthUnit;
         ProtectSystem = "strict";
         ProtectHome = true;
-        PrivateTmp = true;
+        PrivateTmp = "disconnected";
         PrivateDevices = true;
         NoNewPrivileges = true;
         RestrictSUIDSGID = true;