fix: biome config extension missing

[andrea11]

Sorry, with the PR #391, I introduced an issue with biome v2+. The biome CLI refuses configuration if they do not have .json extension.

[andrea11]

Hi @zimbatm, I forgot to update the example. Can you re-approve?

[khaneliman]

Just was coming looking for what caused issue i see after a flake update and this looks like it'd fix it.

nix fmt
ERRO formatter | biome: failed to apply with options '[check --write --no-errors-on-unmatched --config-path /nix/store/sw7wdx5cdqrzdd7vdk7f6p9pf61ilm9d-validated-biome-config]': exit status 1

/nix/store/sw7wdx5cdqrzdd7vdk7f6p9pf61ilm9d-validated-biome-config configuration ━━━━━━━━━━━━━━━━━━━

  × Invalid configuration file. Expected JSON or JSONC file, but got /nix/store/sw7wdx5cdqrzdd7vdk7f6p9pf61ilm9d-validated-biome-config.

[priegger]

I can confirm that this PR fixes the currently broken biome support in main.

Pinning the flake to the commit hash from this branch works for me:

inputs.treefmt-nix.url = "github:numtide/treefmt-nix?rev=d669b561b678d23c40332142573685b0d08225d0";

Pinning the flake to a commit hash before #391 works for me:

inputs.treefmt-nix.url = "github:numtide/treefmt-nix?rev=2673921c03d6e75fdf4aa93e025772608d1482cf";

Using the current main branch does not work for me.