Move mastodon version config to config_for yml (#33577)

spec/presenters/instance_presenter_spec.rb

@@ -68,6 +68,7 @@ RSpec.describe InstancePresenter do
     context 'with the GITHUB_REPOSITORY env variable set' do
       around do |example|
         ClimateControl.modify GITHUB_REPOSITORY: 'other/repo' do
+          reload_configuration
           example.run
         end
       end
@@ -80,6 +81,7 @@ RSpec.describe InstancePresenter do
     context 'without the GITHUB_REPOSITORY env variable set' do
       around do |example|
         ClimateControl.modify GITHUB_REPOSITORY: nil do
+          reload_configuration
           example.run
         end
       end
@@ -88,6 +90,10 @@ RSpec.describe InstancePresenter do
         expect(instance_presenter.source_url).to eq('https://github.com/mastodon/mastodon')
       end
     end
+
+    def reload_configuration
+      Rails.configuration.x.mastodon = Rails.application.config_for(:mastodon)
+    end
   end
 
   describe '#thumbnail' do