gitlab-ci: use ruby 3.2 and latest jekyll

ruby 3.3 fails to build due to google-protobuf dependencies
that cannot be resolved with ruby 3.3:

    An error occurred while installing google-protobuf (3.25.2),
    and Bundler cannot continue.
    In Gemfile:
    jekyll was resolved to 4.3.2, which depends on
        jekyll-sass-converter was resolved to 3.0.0, which depends on
        sass-embedded was resolved to 1.70.0, which depends on
            google-protobuf

Related-to: https://github.com/orgs/community/discussions/82935

.gitlab-ci.yml

@@ -1,12 +1,12 @@
 default:
-  image: ruby@sha256:39d33ab3b46dbfd84609871cf56364d36ba2d9b12731f6bc2fc04afd5274b9d8
+  image: ruby:3.2
   cache:
     paths:
       - vendor/ruby
   before_script:
     - bundle init
     - bundle config set path vendor/ruby
-    - bundle add jekyll --version 4.3.2
+    - bundle add jekyll
     - bundle install
 
 stages: