[Backport] set correct annotation

[gelanivishal]

Original Pull Request

magento#15602

Description

Set correct annotation to formatDateTime function in lib/internal/Magento/Framework/Stdlib/DateTime/TimezoneInterface.php file

Fixed Issues (if relevant)

1. magento/magento2#<15601>: Wrong annotation in formatDateTime - lib/internal/Magento/Framework/Stdlib/DateTime/TimezoneInterface.php

Manual testing scenarios

1. Please review lib/internal/Magento/Framework/Stdlib/DateTime/TimezoneInterface.php
2. Please review lib/internal/Magento/Framework/Stdlib/DateTime/Timezone.php

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)