bugfixes and gem update (#6831)

* update to new version of devise_pam_authenticatable2

* fix behaviour if suffix is nil, fix environment loading, fix user email creation

* code cleanup/fix linter warning

config/application.rb

@@ -16,6 +16,8 @@ require_relative '../lib/devise/ldap_authenticatable'
 
 Dotenv::Railtie.load
 
+Bundler.require(:pam_authentication) if ENV['PAM_ENABLED'] == 'true'
+
 require_relative '../lib/mastodon/redis_config'
 
 module Mastodon