Merge branch '3.4' into 4.3

* 3.4:
  Sync Twig templateExists behaviors
  Fix the :only-of-type pseudo class selector
  [Serializer] Add CsvEncoder tests for PHP 7.4
  Copy phpunit.xsd to a predictable path
  [Security/Http] fix parsing X509 emailAddress
  [Serializer] fix denormalization of string-arrays with only one element #33731
  [Cache] fix known tag versions ttl check

Author: nicolas-grekas

bin/simple-phpunit.php

@@ -110,6 +110,7 @@
         passthru(sprintf('\\' === DIRECTORY_SEPARATOR ? 'rmdir /S /Q %s': 'rm -rf %s', "phpunit-$PHPUNIT_VERSION.old"));
     }
     passthru("$COMPOSER create-project --no-install --prefer-dist --no-scripts --no-plugins --no-progress --ansi phpunit/phpunit phpunit-$PHPUNIT_VERSION \"$PHPUNIT_VERSION.*\"");
+    @copy("phpunit-$PHPUNIT_VERSION/phpunit.xsd", 'phpunit.xsd');
     chdir("phpunit-$PHPUNIT_VERSION");
     if ($SYMFONY_PHPUNIT_REMOVE) {
         passthru("$COMPOSER remove --no-update ".$SYMFONY_PHPUNIT_REMOVE);