@ipv4_dns-search_ignore_auto_routes: set ipv4.dns
The test checks whether the search domains are in effect, but with systemd-resolved that makes little sense unless the link also actually has some nameservers.
In fact NetworkManager ignores the search domains in such case: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/9d8a2d1ba/src/core/dns/nm-dns-manager.c#L1538
Let's just set some nameservers.