document opcache_jit_blacklist

`opcache_jit_blacklist` was added in https://github.com/php/php-src/pull/15559 but seems to be not documented on php.net:

<img width="852" height="700" alt="Image" src="https://github.com/user-attachments/assets/5bb1af95-2483-486a-9966-0c73f1c34fc5" />

see related discussion https://github.com/php/php-src/issues/20458#issuecomment-3519285706