automated: Update flake.lock

- The following Nix Flake inputs were updated:

```
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/3e3afe5174c561dee0df6f2c2b2236990146329f?narHash=sha256-frdhQvPbmDYaScPFiCnfdh3B/Vh81Uuoo0w5TkWmmjU%3D' (2025-06-07)
  → 'github:NixOS/nixpkgs/6e987485eb2c77e5dcc5af4e3c70843711ef9251?narHash=sha256-RKwfXA4OZROjBTQAl9WOZQFm7L8Bo93FQwSJpAiSRvo%3D' (2025-07-16)
```

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

@@ -163,11 +163,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1753250450,
+        "lastModified": 1752687322,
-        "narHash": "sha256-i+CQV2rPmP8wHxj0aq4siYyohHwVlsh40kV89f3nw1s=",
+        "narHash": "sha256-RKwfXA4OZROjBTQAl9WOZQFm7L8Bo93FQwSJpAiSRvo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "fc02ee70efb805d3b2865908a13ddd4474557ecf",
+        "rev": "6e987485eb2c77e5dcc5af4e3c70843711ef9251",
         "type": "github"
       },
       "original": {