Allow bundle updae and tests to be run under ruby 3

Gemfile

@@ -3,8 +3,8 @@
 source 'https://rubygems.org'
 
 require 'json'
-require 'open-uri'
-versions = JSON.parse(open('https://pages.github.com/versions.json').read)
+require 'net/http'
+versions = JSON.parse(Net::HTTP.get(URI('https://pages.github.com/versions.json')))
 
 gem 'github-pages', versions['github-pages']
 

spec/ci_ruby_version_spec.rb

@@ -6,7 +6,7 @@ require 'spec_helper'
 require 'yaml'
 
 describe 'ruby version' do
-  pages_versions = JSON.parse(open('https://pages.github.com/versions.json').read)
+  pages_versions = JSON.parse(URI.open('https://pages.github.com/versions.json').read)
   pages_ruby_version = pages_versions['ruby']
 
   ci_config_file = '.github/workflows/test.yml'