feat: don't use --url in jekyll build

.ci/_config_old.yml

+url: "https://r3.pages.uni.lu"

.ci/deploy.sh

@@ -16,9 +16,12 @@ for branch in $(git for-each-ref --format='%(refname:strip=3)' refs/remotes); do
     git reset --hard $branch
     git pull
 
+    # Generate the config dynamically
+    echo 'url: "https://r3.pages.uni.lu"' > _config_url.yml
+
     # build the website
     bundle install
-    bundle exec jekyll build --url="https://r3.pages.uni.lu" --baseurl="howto-cards/$artefact" -d "build/$artefact"
+    bundle exec jekyll build --config "_config.yml,_config_url.yml" --baseurl="howto-cards/$artefact" -d "build/$artefact"
 
     if [[ $branch == "master" ]]; then
         # set the 404