[Sync EN] ext/soap: document PHP 8.4 changes

PR: `https://github.com/php/doc-en/pull/5735` (2026-08-13)

**Файлы RU для обновления**
- `reference/soap/soapclient.xml`
- `reference/soap/soapclient/construct.xml`
- `reference/soap/soapserver/construct.xml`
- `reference/soap/soapserver/setpersistence.xml`
- `reference/soap/soapvar/construct.xml`

