(maint) Unpin Octokit gem

In 99d7dcb we pinned Octokit to 4.21.0 due to an issue with
authentication and the Faraday gem in Octokit 4.22.0. There was
a fix for this issue in 4.23.0, so we no longer need to pin back.

This gem is used to generate changelogs in release prep, and other
modules (i.e. Puppet core modules) have used newer versions of
Octokit (4.25.0) without issue.

This commit removes the pin for Octokit to 4.21.0.

Author: mhashizume

.sync.yml

@@ -39,8 +39,6 @@ Gemfile:
       - gem: 'beaker-task_helper'
         version: '~> 1.9'
         condition: 'ENV["GEM_BOLT"]'
-      - gem: octokit
-        version: '4.21.0' # due to https://github.com/octokit/octokit.rb/issues/1391
       - gem: async
         version: '~> 1.30' # otherwise async 2.0.0(needs ruby >=3.1.0) is wrongly selected by bundler on jenkins while running with ruby 2.7.1
       - gem: puppet_litmus

Gemfile

@@ -48,7 +48,6 @@ group :development do
   gem "nokogiri",                                                               require: false
   gem "bolt", '~> 3.0',                                                         require: false if ENV["GEM_BOLT"]
   gem "beaker-task_helper", '~> 1.9',                                           require: false if ENV["GEM_BOLT"]
-  gem "octokit", '4.21.0',                                                      require: false
   gem "async", '~> 1.30',                                                       require: false
 end
 group :system_tests do