chore: bump github-pages gem to ~> 232 to match GitHub Pages CI

GitHub Pages upgraded the github-pages gem to v232, which no longer
satisfies the '~> 228' constraint in the Gemfile and causes the
pages build workflow to fail with 'The github-pages gem can't
satisfy your Gemfile's dependencies'.

Bumping the constraint to '~> 232' and removing the stale Gemfile.lock
so the Pages CI regenerates it against the new resolver.

Author: jupyterj0nes

Gemfile

@@ -1,6 +1,6 @@
 source "https://rubygems.org"
 
-gem "github-pages", "~> 228", group: :jekyll_plugins
+gem "github-pages", "~> 232", group: :jekyll_plugins
 
 group :jekyll_plugins do
   gem "jekyll-feed", "~> 0.12"