bug#59515: nginx: Fails to start on boot while upstream service is not yet running

[Jonathan Brielmaier <jonathan.brielmaier@web.de>]

Ah thanks.

I added `(shepherd-requirement '(radicale))` to my nginx-configuration.
Sadly the issue is not fixed, the situation is the same as before.

I assume that radicale takes a fracture of a second to start. And nginx
starts faster up. See this small experiment:

$ sudo herd stop radicale
$ sudo herd start radicale; curl localhost:5232
Service radicale has been started.
curl: (7) Failed to connect to localhost port 5232 after 0 ms:
Verbindungsaufbau abgelehnt

$ sudo herd stop radicale
$ sudo herd start radicale; sleep 0.2; curl localhost:5232
Service radicale has been started.
Redirected to /.web