build.yaml: upgrade actions

in case this indirectly fixes SSL error in #40

Author: dhimmel

.github/workflows/build.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
         with:
@@ -23,7 +23,7 @@ jobs:
         run: bundle exec jekyll build
       - name: Deploy website
         if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request' && !github.event.repository.fork
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: _site