docs: update worker.md to prevent infinite loop (#455)
* Update worker.md to prevent infinite loop
Quick fix typo `<=` rather than `>=` which prevents infinite loop and get out of the loop when MAX_REQUESTS is reached.
* Update worker.md to fix impossible evaluation
Fix impossible case where if MAX_REQUESTS is not defined the rest of the condition is not evaluated as it is an && operator as mentioned by https://github.com/dunglas/frankenphp/discussions/453#discussioncomment-7981535
* Update worker.md change to for loop and remove handler from the loop
Change to for loop and remove handler from the loop based on the feedback https://github.com/dunglas/frankenphp/pull/455#discussion_r1438918811
