automated: Update flake.lock

- The following Nix Flake inputs were updated:

```
• Updated input 'nixpkgs':
    'path:/nix/store/jk6xpbfh10gz6q5cqw8b2f7xk0pl7hkv-source?lastModified=1741010256&narHash=sha256-WZNlK/KX7Sni0RyqLSqLPbK8k08Kq7H7RijPJbq9KHM%3D&rev=ba487dbc9d04e0634c64e3b1f0d25839a0a68246' (2025-03-03)
  → 'github:NixOS/nixpkgs/18dd725c29603f582cf1900e0d25f9f1063dbf11?narHash=sha256-awS2zRgF4uTwrOKwwiJcByDzDOdo3Q1rPZbiHQg/N38%3D' (2025-04-13)
```

Auto-generated by [update.yml][1] with the help of
[create-pull-request][2].

[1]: https://forgejo.stefka.eu/jiriks74/nix.nvim/src/branch/main/.github/workflows/update.yml
[2]: https://forgejo.stefka.eu/jiriks74/create-pull-request

flake.lock

@@ -20,11 +20,12 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1741010256,
-        "narHash": "sha256-WZNlK/KX7Sni0RyqLSqLPbK8k08Kq7H7RijPJbq9KHM=",
-        "path": "/nix/store/jk6xpbfh10gz6q5cqw8b2f7xk0pl7hkv-source",
-        "rev": "ba487dbc9d04e0634c64e3b1f0d25839a0a68246",
-        "type": "path"
+        "lastModified": 1744536153,
+        "narHash": "sha256-awS2zRgF4uTwrOKwwiJcByDzDOdo3Q1rPZbiHQg/N38=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "18dd725c29603f582cf1900e0d25f9f1063dbf11",
+        "type": "github"
       },
       "original": {
         "id": "nixpkgs",