test: convert to ESLint Flat config

[MikeMcC399]

Current situation

eslint.config.mjs relies on using import { FlatCompat } from '@eslint/eslintrc' to run eslint-plugin-cypress.

Starting with eslint-plugin-cypress@3.3.0 the plugin has full support for Flat config files using:

import pluginCypress from 'eslint-plugin-cypress/flat'
export default [
  pluginCypress.configs.recommended
]

Change

1. Remove @eslint/eslintrc
2. Add eslint-plugin-cypress/flat

Verification

npm ci
npm run lint

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[cypress-app-bot]

🎉 This PR is included in version 3.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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