Fix building with Jekyll on Ruby 3.4 (#1079)

Ruby 3.4 removed several standard library packages, so they have
to be installed as gems instead.

This also updates Jekyll to use a version that's supported in Ruby 3.4.

The minimum required Ruby version is now 3.2.

.github/workflows/build-pr.yml

@@ -18,10 +18,10 @@ jobs:
 
     # Configure the build environment.
 
-    - name: Install Ruby 3.1
+    - name: Install Ruby 3.2
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: '3.1'
+        ruby-version: '3.2'
         # Runs 'bundle install' and caches installed gems automatically
         bundler-cache: true
 
@@ -34,7 +34,7 @@ jobs:
       run: bundle exec jekyll build
 
     # Upload resulting "_site" directory as artifact
-    
+
     - uses: actions/upload-artifact@v4
       with:
         name: site

.github/workflows/build-website.yml

@@ -23,10 +23,10 @@ jobs:
 
     # Configure the build environment.
 
-    - name: Install Ruby 3.1
+    - name: Install Ruby 3.2
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: '3.1'
+        ruby-version: '3.2'
         # Runs 'bundle install' and caches installed gems automatically
         bundler-cache: true