Merge branch '6.4' into 7.4

* 6.4:
  Drop PR warning and auto-closing on subtree splits
  Fix merge
  Remove review state from Serbian translations
  [Translation] Copy domains metadata when moving messages to intl ones
  [Form] Add missing translation for invalid UUID
  fix(translations): fix sr-Latn validation messages and video constrai…
  [Validator] Add translated messages for the XML constraint
  Update installation command for Stopwatch component
  [Notifier] Send message to MS-Teams via Workflow.
  [Mailer] Fix inline images in MandrillApiTransport by using the Content-ID as image name
  [Form] Translate TranslatableInterface label in violation messages
  [Security][HttpKernel] Add allowed_classes => false to unserialize() in CacheWarmerAggregate, LoggerDataCollector, and HttpCache Store
  Fix XMLHttpRequest URL handling in toolbar JS

Author: nicolas-grekas