Raise Mastodon::HostValidationError when host for HTTP request is private (#6410)

config/environments/development.rb

@@ -85,3 +85,9 @@ Rails.application.configure do
 end
 
 ActiveRecordQueryTrace.enabled = ENV.fetch('QUERY_TRACE_ENABLED') { false }
+
+module PrivateAddressCheck
+  def self.private_address?(*)
+    false
+  end
+end