Switch darktable to unstable channel

So i can get on the 5.4 release.

flake.lock

@@ -74,6 +74,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1766651565,
+        "narHash": "sha256-QEhk0eXgyIqTpJ/ehZKg9IKS7EtlWxF3N7DXy42zPfU=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "3e2499d5539c16d0d173ba53552a4ff8547f4539",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs_2": {
       "locked": {
         "lastModified": 1765838191,
@@ -94,7 +110,8 @@
       "inputs": {
         "home-manager": "home-manager",
         "locutus": "locutus",
-        "nixpkgs": "nixpkgs_2"
+        "nixpkgs": "nixpkgs_2",
+        "nixpkgs-unstable": "nixpkgs-unstable"
       }
     },
     "systems": {