指定しないと、composerのDockerイメージで `composer install`
を実行したときに下記のエラーが起きてしまう。
(ただし、--no-dev オプションをつけると発生しない)

  Problem 1
    - phpdocumentor/reflection-docblock is locked to version 5.1.0 and
      an update of this package was not requested.
    - phpdocumentor/reflection-docblock 5.1.0 requires ext-filter ^7.1
      -> it has the wrong version installed (8.1.5).
  Problem 2
    - phpdocumentor/reflection-docblock 5.1.0 requires ext-filter ^7.1
      -> it has the wrong version installed (8.1.5).
    - phpspec/prophecy v1.10.3 requires
      phpdocumentor/reflection-docblock ^2.0|^3.0.2|^4.0|^5.0 ->
satisfiable by phpdocumentor/reflection-docblock[5.1.0].
    - phpspec/prophecy is locked to version v1.10.3 and an update of
      this package was not requested.

CIでエラーが起きていた
ref https://github.com/pepabo/colormeshop-wp-plugin/runs/5071978852?check_suite_focus=true

当該プラグインのドキュメント:
https://github.com/PHPCSStandards/composer-installer#usage
> When using Composer 2.2 or higher, Composer will ask for your
permission to allow this plugin to execute code.