htmlpageheader - bolding unicode

[MoVoDesign]

Prerequisites

• [x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• [x] The issue still exists against the latest master branch of yii2-mpdf.
• [x] This is not an usage question. I confirm having gone through and read the documentation.
• [x] This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
• [x] I have attempted to find the simplest possible steps to reproduce the issue.
• [ ] I have included a failing test as a pull request (Optional).

Steps to reproduce the issue

1. render a ('mode' => Pdf::MODE_UTF8) pdf with content:

    <htmlpageheader name="otherpages">
    <b>a 記試</b> / <i>b 記試</i> / <span style="font-weight: bold">c 記試</span>
    </htmlpageheader>

Expected behavior and actual behavior

When I follow those steps, I see the Chinese characters above with normal font weight: a 記試

I was expecting bold font-weight: a 記試

Please note Bold Chinese fonts work in other parts of the pdf generated

Environment

OSX 12.6 / PHP 8.0.23

yiisoft/yii2                          2.0.46
kartik-v/yii2-mpdf             dev-master 6a6506e

Browsers

• [x] Google Chrome
• [ ] Mozilla Firefox
• [ ] Internet Explorer
• [x] Safari

Operating System

• [ ] Windows
• [x] Mac OS X
• [x] Linux (CentOS)
• [ ] Mobile

Libraries

• jQuery version: 2.1.4
• yii2-mpdf version: dev-master 6a6506e

Isolating the problem

• [ ] This bug happens on the demos page
• [x] The bug happens consistently across all tested browsers
• [ ] This bug happens when using yii2-mpdf without other plugins (no other PDF plugins)