build(deps): bump actions/checkout from 2 to 3

This reverts commit e07c00b807.

.github/dependabot.yml

@@ -5,3 +5,8 @@ updates:
     schedule:
       interval: "daily"
 
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+

.github/workflows/html5validator.yml

@@ -0,0 +1,26 @@
+name: HTML5 Validator
+
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v3 # Required will all actions
+
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: 3.1
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+
+    - name: Jekyll build
+      run: |
+        bundle exec jekyll build --drafts --profile
+
+    - name: Checks HTML5 validity
+      uses: Cyb3r-Jak3/html5validator-action@v7.1.1
+      with:
+        root: _site/
+        blacklist: n r or ir