chore: Replace deprecated next lint command with eslint .

[torokati44]

See:

• https://nextjs.org/blog/next-15-5#next-lint-deprecation
• https://github.com/ruffle-rs/ruffle-rs.github.io/actions/runs/18838470831/job/53744860304#step:7:9
• https://nextjs.org/blog/next-16#removals
• https://github.com/ruffle-rs/ruffle-rs.github.io/actions/runs/18838824384/job/53746041192?pr=460#step:7:9

[torokati44]

This is to unblock #460, #461, and #462.

But, uhm... help? 🥺 @danielhjacobs I can't make CI turn green.

[danielhjacobs]

Try marking those files as CommonJS:

  {
    files: ["postcss.config.js", "next.config.js"],
    languageOptions: {
      sourceType: "commonjs",
    },
  },

By default, an ESLint mjs file treats all files it lints as ECMAScript modules: https://eslint.org/docs/latest/use/configure/configuration-files#configuration-objects, but those files are written with vanilla JS syntax. I suppose maybe you can make them mjs config files, but that's a somewhat larger change.

[torokati44]

Oh, nice, thanks for the fix! Just noticed it now, sorry...