Migrate GitHub Pages deployment from CircleCI to GitHub Actions

CircleCI deploy was failing due to an expired SSH deploy key. Replace
the entire pipeline with a GitHub Actions workflow using native Pages
deployment — no keys or tokens needed. Also bump action versions in
the spell checking workflow.

Author: bbatsov

.circleci/config.yml

@@ -0,0 +1,42 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [master]
+
+permissions:
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+      - name: Install AsciiDoctor & Rouge
+        run: gem install asciidoctor rouge
+      - name: Build site
+        run: |
+          mkdir -p _build/html
+          asciidoctor -a toc="left" -a toclevels=2 README.adoc -o _build/html/index.html
+          touch _build/html/.nojekyll
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: _build/html
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4

.github/workflows/deploy.yml

@@ -10,9 +10,9 @@ jobs:
       matrix:
         python-version: [3.8]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
@@ -26,7 +26,7 @@ jobs:
     name: Check spelling with misspell
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install
         run: wget -O - -q https://git.io/misspell | sh -s -- -b .
       - name: Misspell