Merge branch '6.4' into 7.0

* 6.4:
  [Validator] Missing translations for Estonian (et)
  [HttpFoundation] Prevent duplicated headers when using Early Hints
  [VarDumper] Fix configuring CliDumper with SYMFONY_IDE env var
  [Cache] improve BC with 5.4 pools
  [PhpUnitBridge][VarDumper] fix color detection
  [CI] Make sure we preserve file->header when we run sync-translations.php
  [Cache] Fix BC layer with pre-6.1 cache items
  Review validators.sl.xlf
  [Mailer][Postmark][Webhook] Don't require tag and metadata
  [Scheduler] Fix messenger receiver with no alias

DeprecationErrorHandler.php

@@ -403,7 +403,7 @@ private static function hasColorSupport(): bool
         // Detect msysgit/mingw and assume this is a tty because detection
         // does not work correctly, see https://github.com/composer/composer/issues/9690
         if (!@stream_isatty(\STDOUT) && !\in_array(strtoupper((string) getenv('MSYSTEM')), ['MINGW32', 'MINGW64'], true)) {
-            return true;
+            return false;
         }
 
         if ('\\' === \DIRECTORY_SEPARATOR && @sapi_windows_vt100_support(\STDOUT)) {