Fix site page deploy

Our .gitlab-ci is configured to use the latest ruby version to run its jobs (including the pages deploy job). Moreover, gitlab CI takes into account the Bundler version used to generate the project's Gemfile.lock and tries to use that Bundler version to run each job.

Our current Gemfile.lock bundler is Bundler 1.17, which uses Pathname#untaint, a deprecated function that was removed in Ruby 3.2. Since gitlab pages latest ruby docker image now runs with ruby 3.2.0, the absence of Pathname#untaint leads to a deploy error.

Update the gitlab-ci to use ruby 3.0. Also, embed the image keyword within a default global keyword as noted in gitlab documentation 1.

Despite this change, our deploy job won't succeed because (strangely) gitlab CI ruby 3.0 docker image can't find 'bundler' (1.17.2). So, we have an additional commit for updating the project's Blundler from 1.17.2 to 2.3.8. Regenerating the Gemfile.lock also had the side effect of updating a few ruby gems and the ruby version itself (from 2.6 to 3.0).

It would be wonderful if ruby and ruby gems could keep compatibility when updating to newer versions. Though, we all know that's a dream that ruby developers won't let come true. Also, updating ruby and ruby gems seems to be inevitable because sooner or later gitlab CI or some gem will probably force us to update the whole thing. This is the update for now.

Signed-off-by: Marcelo Schmitt marcelo.schmitt1@gmail.com