change auto scrub time to weekly

nixos/server/zfs.nix

···
 {
   services.zfs = {
     trim.enable = true;
-    autoScrub.enable = true;
+		autoScrub = {
+			enable = true;
+			interval = "weekly";
+		};
     autoSnapshot.enable = true;
     zed = {
       settings = {