034: build docs with bundler instead of jekyll-build-pages

The actions/jekyll-build-pages action only supports the small set of
themes bundled with the github-pages gem (minima, slate, etc.). It
cannot resolve just-the-docs, which fails the build with:

  The just-the-docs theme could not be found.

Switch to ruby/setup-ruby + bundle exec jekyll build so the Gemfile
is honored. Pin jekyll ~> 4.3 and just-the-docs ~> 0.10.

Author: angelovstanton

.github/workflows/docs.yml

@@ -23,21 +23,33 @@ concurrency:
 jobs:
   build:
     runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: docs
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
+          working-directory: docs
+
       - name: Setup Pages
+        id: pages
         uses: actions/configure-pages@v5
 
       - name: Build with Jekyll
-        uses: actions/jekyll-build-pages@v1
-        with:
-          source: ./docs
-          destination: ./_site
+        run: bundle exec jekyll build --baseurl "${{ steps.pages.outputs.base_path }}"
+        env:
+          JEKYLL_ENV: production
 
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/_site
 
   deploy:
     environment:

docs/Gemfile

@@ -1,4 +1,12 @@
 source "https://rubygems.org"
 
-gem "jekyll-seo-tag"
-gem "just-the-docs"
+gem "jekyll", "~> 4.3"
+gem "just-the-docs", "~> 0.10"
+gem "jekyll-seo-tag", "~> 2.8"
+
+# Windows / JRuby support (no-op on Linux runners)
+platforms :mingw, :x64_mingw, :mswin, :jruby do
+  gem "tzinfo", ">= 1", "< 3"
+  gem "tzinfo-data"
+  gem "wdm", "~> 0.1"
+end