Add a new GH workflow for deploying to GH pages (#938)

.github/workflows/gh-pages.yml

@@ -0,0 +1,47 @@
+name: Deploy IRB documentation to GitHub Pages
+
+on:
+  push:
+    branches: ["master"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: ${{ github.repository == 'ruby/irb' && !startsWith(github.event_name, 'pull') }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@1198b074305f9356bd56dd4b311757cc0dab2f1c # v1.175.1
+        with:
+          ruby-version: "3.3"
+          bundler-cache: true
+      - name: Setup Pages
+        id: pages
+        uses: actions/configure-pages@v5
+      - name: Build with IRB
+        # Outputs to the './_site' directory by default
+        run: bundle exec rake rdoc
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4