PDF fails after updating past 3.0.15

[pixelmachine]

Describe the bug

I recently updated from 3.0.15 to 3.0.18 and PDF generation stopped working with an error:
"Undefined array key ''" on line 4752 in dompdf\dompdf\lib\Cpdf.php
The stack trace points to this line:
$font = $this->fonts[$this->currentFont];

I found an issue on dompdf but it doesn't really help as those options are not exposed in Gift Voucher.

• PDF generation from Commerce (like an order receipt) still works fine.
• Downgrading to 3.0.15 restored the functionality
• This is on a linux cloud host but not Craft Cloud

I can see some changes were made around 3.0.16 for Craft Cloud PDFs so I assume they are the culprit.

Steps to reproduce

1. Install 3.0.18
2. Download a PDF
3. See an error

Craft CMS version

4.16.11

Plugin version

3.0.18

Multi-site?

Yes

[engram-design]

Related to #138 and craftcms/commerce#3983

Should be fixed for the next release. To get this early, run composer require verbb/gift-voucher:"dev-craft-4 as 3.0.18".