nix: fix a bug where inputs and their configs where being ignored

Fixed upstream by allowing Nix to read `.devenv/devenv.json`.

Author: sandydoo

devenv.lock

@@ -150,10 +150,10 @@
         "pre-commit-hooks": "pre-commit-hooks"
       },
       "locked": {
-        "lastModified": 1745500508,
+        "lastModified": 1745930071,
         "owner": "domenkozar",
         "repo": "nix",
-        "rev": "090394819020afda8eae69e395b1accba9c0fab2",
+        "rev": "b455edf3505f1bf0172b39a735caef94687d0d9c",
         "type": "github"
       },
       "original": {