[ticket/12402] CAPTCHA plugin migration fails to detect missing plugins

PHPBB3-12402
Merge pull request #2418 from Nicofuma/ticket/12402

[ticket/12402] CAPTCHA plugin migration fails to detect missing plugins

* Nicofuma/ticket/12402:
  [ticket/12402] CAPTCHA plugin migration fails to detect missing plugins
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12402] CAPTCHA plugin migration fails to detect missing plugins