Keep at least 15 days of cache

.forgejo/workflows/auto-update-build.yaml

@@ -153,5 +153,4 @@ jobs:
       - name: Cleanup
         if: always()
         run: |
-          nix-collect-garbage -d
           rm -rf result .direnv

hosts/forgejo-runner/default.nix

@@ -17,7 +17,10 @@ in
 
   my = {
     utils = {
-      commons.enable = true;
+      commons = {
+        enable = true;
+        gc.enable = false;
+      };
       lxc-standard.enable = true;
     };
 
@@ -35,6 +38,12 @@ in
     virtualisation.proxmox.enable = true;
   };
 
+  nix.gc = {
+    automatic = true;
+    dates = "daily";
+    options = "--delete-older-than 15d";
+  };
+
   # Extra packages needed for CI operations
   environment.systemPackages = with pkgs; [
     git