Can't change user agent for firefox/geckodriver

I'm trying to set a specific User-Agent in geckodriver for the sake of my tests. But I can't find how to properly set that option in yml settings.

Is there any way to change for firefox the user agent?

* Codeception version: 5.1
* PHP Version: 8.2
* Operating System: Ubuntu
* Installation type: Composer
* Suite configuration:

```yml
wpfirefox:
modules:
enabled:
config:
WPWebDriver:
url: '%TEST_LOCAL_WP_URL%'
adminUsername: '%TEST_WP_ADMIN_USERNAME%'
adminPassword: '%TEST_WP_ADMIN_PASSWORD%'
adminPath: '%TEST_WP_ADMIN_PATH%'
browser: firefox
path: ''
window_size: 1024x768
capabilities:
moz:firefoxOptions:
args: ["-user-agent=wp-browser", "-headless"]
prefs:
intl.accept_languages: "fr-FR"
```

从 WPWebDriver 套件配置及其 capabilities 条目开始，重点检查 issue 中所示的 moz:firefoxOptions args 和 prefs。使用 Firefox 复现该配置，并确定是否应用了请求的 user agent；完成的标准是测试浏览器报告已配置的 User-Agent，同时保留现有的 language 和 headless 设置。

由索引模型根据 Issue 内容生成。