[CI] Fix build-github-pages CI job

Recent updates to the pages-gem repository, used by the
build-github-pages CI job, have introduced a regression by which the
build fails due to incompatible Ruby version.

We'll fix this by passing in a specific Ruby version that's compatible.

tools/build-github-pages.sh

@@ -34,9 +34,9 @@ set -x
 ROOTDIR=$(realpath "$(dirname "$(realpath "$0")")/..")
 TEMPDIR=$(mktemp -d)
 cd $TEMPDIR
-git clone https://github.com/github/pages-gem.git
+git clone --depth 1 https://github.com/github/pages-gem.git
 cd pages-gem
-make image
+docker build -t gh-pages --build-arg RUBY_VERSION=3.2 .
 cd $ROOTDIR
 echo -e "plugins:\n \
         - jekyll-coffeescript\n \