Stop testing stable nixos

We only test and support matching nixpkgs versions to simpliy alignment
with breaking changes on nixos unstable.

flake.lock

@@ -93,29 +93,12 @@
         "type": "github"
       }
     },
-    "nixpkgs-25_05": {
-      "locked": {
-        "lastModified": 1761999846,
-        "narHash": "sha256-IYlYnp4O4dzEpL77BD/lj5NnJy2J8qbHkNSFiPBCbqo=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "3de8f8d73e35724bf9abef41f1bdbedda1e14a31",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixos-25.05",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "root": {
       "inputs": {
         "blobs": "blobs",
         "flake-compat": "flake-compat",
         "git-hooks": "git-hooks",
-        "nixpkgs": "nixpkgs",
-        "nixpkgs-25_05": "nixpkgs-25_05"
+        "nixpkgs": "nixpkgs"
       }
     }
   },