nixos/tests: fix curl-impersonate under network-online dep fix

Changed files
+2
nixos
+2
nixos/tests/curl-impersonate.nix
···
start_all()
with subtest("Wait for network"):
+
web.systemctl("start network-online.target")
+
curl.systemctl("start network-online.target")
web.wait_for_unit("network-online.target")
curl.wait_for_unit("network-online.target")