Incorrect encoding when exporting to pdf #5872

Attempted Debugging

• I have read the debugging page

Searched GitHub Issues

• I have searched GitHub for the issue.

Describe the Scenario

Hi! When exporting a document in PDF format, the encoding of the headings breaks: in Cyrillic, I see "?????" instead.
I searched for a solution on Github, but couldn't find one. Please, help me: what's wrong and what can be fixed?

Exact BookStack Version

BookStack v25.07

Log Content

Hosting Environment

Ubuntu 22.04,
PHP 8.3.19,
~# locale
LANG=ru_RU.UTF-8
LANGUAGE=
LC_CTYPE="ru_RU.UTF-8"
LC_NUMERIC="ru_RU.UTF-8"
LC_TIME="ru_RU.UTF-8"
LC_COLLATE="ru_RU.UTF-8"
LC_MONETARY="ru_RU.UTF-8"
LC_MESSAGES="ru_RU.UTF-8"
LC_PAPER="ru_RU.UTF-8"
LC_NAME="ru_RU.UTF-8"
LC_ADDRESS="ru_RU.UTF-8"
LC_TELEPHONE="ru_RU.UTF-8"
LC_MEASUREMENT="ru_RU.UTF-8"
LC_IDENTIFICATION="ru_RU.UTF-8"
LC_ALL=