Add automated testing for publish action

Creates a test workflow that generates a documentation website from the
repository READMEs and publishes it to gh-pages. This tests the full
publish action workflow including the worktree credential handling.

The workflow:
- Runs on push to main and manual dispatch
- Dynamically generates Quarto site from READMEs via heredoc
- Fixes relative links to work in the rendered site
- Publishes to gh-pages, testing the complete worktree code path

Also creates a minimal documentation site at quarto-dev.github.io/quarto-actions/
as a useful side benefit.

Author: cderv

.github/docs/_quarto.yml

@@ -0,0 +1,16 @@
+project:
+  type: website
+
+website:
+  title: "Quarto Actions"
+  navbar:
+    left:
+      - text: "Setup"
+        href: setup.qmd
+      - text: "Render"
+        href: render.qmd
+      - text: "Publish"
+        href: publish.qmd
+    right:
+      - icon: github
+        href: https://github.com/quarto-dev/quarto-actions

.github/workflows/test-publish.yaml

@@ -0,0 +1,102 @@
+name: Test Publish Action
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+jobs:
+  test-publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: ./setup
+        with:
+          version: release
+
+      # Generate website content from README files
+      - name: Generate Quarto site
+        run: |
+          # Create working directory structure
+          mkdir -p _site_source
+
+          # Copy Quarto config
+          cp .github/docs/_quarto.yml _site_source/
+
+          # Define repo URL for link fixing
+          REPO_URL="https://github.com/quarto-dev/quarto-actions"
+
+          # Function to fix links in a README
+          fix_readme_links() {
+            local file=$1
+            # First: Fix known action page links to point to site pages
+            sed -i \
+              -e 's|\](./setup)|\](setup.qmd)|g' \
+              -e 's|\](./render)|\](render.qmd)|g' \
+              -e 's|\](./publish)|\](publish.qmd)|g' \
+              "$file"
+            # Second: All remaining ./ links point to GitHub
+            sed -i "s|\](./|\](${REPO_URL}/tree/main/|g" "$file"
+          }
+
+          # Copy and fix main README
+          cp README.md _site_source/
+          fix_readme_links _site_source/README.md
+
+          # Copy and fix action READMEs
+          cp setup/README.md _site_source/setup-readme.md
+          fix_readme_links _site_source/setup-readme.md
+
+          cp render/README.md _site_source/render-readme.md
+          fix_readme_links _site_source/render-readme.md
+
+          cp publish/README.md _site_source/publish-readme.md
+          fix_readme_links _site_source/publish-readme.md
+
+          # Generate index.qmd
+          cat > _site_source/index.qmd <<'EOF'
+          ---
+          title: "Quarto Actions"
+          ---
+
+          This site demonstrates the quarto-actions and tests the publish action.
+
+          {{< include README.md >}}
+          EOF
+
+          # Generate action pages
+          cat > _site_source/setup.qmd <<'EOF'
+          ---
+          title: "Setup Action"
+          ---
+
+          {{< include setup-readme.md >}}
+          EOF
+
+          cat > _site_source/render.qmd <<'EOF'
+          ---
+          title: "Render Action"
+          ---
+
+          {{< include render-readme.md >}}
+          EOF
+
+          cat > _site_source/publish.qmd <<'EOF'
+          ---
+          title: "Publish Action"
+          ---
+
+          {{< include publish-readme.md >}}
+          EOF
+
+      # Test the publish action
+      - uses: ./publish
+        with:
+          target: gh-pages
+          path: _site_source
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}