flake: use latest nil lsp

flake.lock

@@ -641,6 +641,26 @@
         "type": "github"
       }
     },
+    "nil": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1750558251,
+        "narHash": "sha256-wmb+kcqG05jQA2RPq+KZhOeCxSEOAgumgp/remOsczs=",
+        "owner": "oxalica",
+        "repo": "nil",
+        "rev": "4e5ac6ec65c775fbc6adba1c6022b29c7eccde0f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "nil",
+        "type": "github"
+      }
+    },
     "nix-filter": {
       "locked": {
         "lastModified": 1731533336,
@@ -955,6 +975,7 @@
         "latest": "latest",
         "lix": "lix",
         "lix-module": "lix-module",
+        "nil": "nil",
         "nix-index-database": "nix-index-database",
         "nix-minecraft": "nix-minecraft",
         "nixos-hardware": "nixos-hardware",