[Sync EN] Update `ReturnTypeWillChange` intro for clarity

[github-actions]

PR: https://github.com/php/doc-en/pull/5614 (2026-07-24)

Файлы RU для обновления

• language/predefined/attributes/returntypewillchange.xml
• reference/reflection/reflectionfunctionabstract/gettentativereturntype.xml
• reference/reflection/reflectionfunctionabstract/hastentativereturntype.xml