gc: change to older than 30

the old +3 did not seem to work

hosts/common/global/nix.nix

@@ -2,7 +2,8 @@
   lib,
   outputs,
   ...
-}: {
+}:
+{
   # Apply overlays
   nixpkgs = {
     # TODO: apply this to hm and nixos without duplicate code
@@ -31,12 +32,11 @@
   nix.gc = {
     automatic = true;
     dates = "weekly";
-    # Keep the last 3 generations
-    options = "--delete-older-than +3";
+    options = "--delete-older-than 30d";
   };
   nix.optimise = {
     automatic = true;
-    dates = ["weekly"]; # Optional; allows customizing optimisation schedule
+    dates = [ "weekly" ]; # Optional; allows customizing optimisation schedule
   };
 
   programs.nix-ld.enable = true;