nixos/k3s: run etcd test with correct k3s package

Changed files
+1
nixos
tests
k3s
+1
nixos/tests/k3s/etcd.nix
···
services.k3s = {
enable = true;
role = "server";
+
package = k3s;
extraFlags = [
"--datastore-endpoint=\"http://192.168.1.1:2379\""
"--disable coredns"