v5 - FlatConfig, ESM, eslint-remote-tester@v4

This major release adds support for eslint-remote-tester@v4 and ESLint's FlatConfig. Node version was updated from 18 to 20.

What's Changed

• feat!: support eslint-remote-tester@v4, ESM & FlatConfig by @AriPerkkio in #33
• feat!: use node 20 by @AriPerkkio in 5724813

Full Changelog: v4.1.0...v5