UI Toolkit doesn't render the assigned sprites when using unicode characters assigned to a sprite

How to reproduce:
1. Open the attached "IN-140438_ui-toolkit-bug.zip" project
2. Open the "SampleScene"
3. Open the Game view tab
4. Observe the "Unicode characters >>> <<<" text in the top left corner

Actual result: No characters are rendered within the ">>> <<<" part of the text
Expected result: Custom characters are rendered within the ">>> <<<" part of the text (as in text example above)

Reproducible with: 2023.2.0b4, 6000.0.74f1, 6000.3.14f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a4
Not reproducible with: 2023.2.0b3

Reproducible on: Windows 11
Not reproducible on: No other environments tested