Fix deploy workflow - update deprecated GitHub Actions syntax

[Copilot]

The deploy workflow was using deprecated GitHub Actions syntax (set-output) and outdated action versions that caused deployment failures.

Changes

• Removed deprecated set-output command - Eliminated manual yarn cache directory detection
• Updated actions - checkout@v2.3.1 → v4, replaced cache@v2 with setup-node@v4 built-in caching
• Updated deployment action - github-pages-deploy-action@v3.7.1 → v4 with lowercase parameters (branch, folder, clean)
• Added permissions - contents: write for deployment authorization

Before

- name: Get yarn cache directory 📦
  id: yarn-cache
  run: |
    echo "::set-output name=dir::$(yarn cache dir)"

- name: Deploy 🚀
  uses: JamesIves/github-pages-deploy-action@3.7.1
  with:
    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    BRANCH: gh-pages
    FOLDER: build

After

- name: Setup Node.js
  uses: actions/setup-node@v4
  with:
    node-version: '18'
    cache: 'yarn'

- name: Deploy 🚀
  uses: JamesIves/github-pages-deploy-action@v4
  with:
    branch: gh-pages
    folder: build

Original prompt

The deploy task seems to be broken (this is a pretty old repo)

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