pkgfile-update.service: Add After=nss-lookup.target

[thiagowfx]

This is a follow-up of https://github.com/falconindy/pkgfile/pull/51 ("Make systemd unit depend on network-online.target") that enhances the unit file with After=nss-lookup.target.

This is needed as per https://wiki.archlinux.org/title/systemd#Running_services_after_the_network_is_up:

From systemd.special(7): "All services for which the availability of full host/network name resolution is essential should be ordered after this target, but not pull it in."

[thiagowfx]

To give more context: This originally surfaced on https://lists.archlinux.org/pipermail/pacman-contrib/2021-July/000379.html, which adds a similar unit for pacman -Fy. Someone suggested this improvement there, and I believe it's equally applicable here.

[falconindy]

Merged as 37a483f11a73a.