ci: update `actions/checkout` from v2 to v3 in our GitHub workflows (#499)

## 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

<!--- Put an `x` in all the boxes that apply: -->

- [ ] ✨ 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

Co-authored-by: Álvaro Stivi <astivi@users.noreply.github.com>

.github/workflows/spell_check.yaml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Check spelling
         uses: zwaldowski/cspell-action@v1