[modules/base-system] Make nix garbage collection less aggressive

modules/base-system.nix

@@ -105,11 +105,10 @@
     };
     networking.firewall.allowedUDPPorts = [config.services.tailscale.port];
 
-    # Regularly clear the store, since the storage is quite small
-    # The store is optimized ~04:00, so let's clear it before that
+    # Regularly clear the store
     nix.gc = {
       automatic = true;
-      dates = "03:00";
+      dates = lib.mkDefault "weekly";
     };
     # Enable store optimiser
     nix.optimise = {