ci: update `actions/checkout` from v2 to v3 in our GitHub workflows

[nilsreichardt]

Description

Node 12 is deprecated for GitHub Actions. This is the reason why we are getting a warning from GitHub:

Node.js 12 actions are deprecated. Please update the following actions to use Node.js 16: actions/checkout@v2. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/.

This PR updates actions/checkout from v2 to v3 which should fix the problem.

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [x] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

[Hixie]

What's the status of this PR?

[nilsreichardt]

What's the status of this PR?

A review is missing