Glyphs from TTF files are no longer rendered correctly on glow signs

This behavior was introduced in 25w09a.

The bug

When loading a font from a ttf file in a resource pack, the text isn't rendered correctly on glowing signs. The shape of the characters is correct, but the highlighting doesn't correctly appear behind the text, instead overlapping with it. Only the characters that are changed by the ttf file are affected.

Steps to reproduce

1. Load the [mediaInline] resource pack (or any resource pack that uses a ttf font).

2. Paste the text from [mediaInline] (or any character changed by a resource pack using a ttf font) into a sign.

3. Use a glow ink sac on the sign.

Observed behavior

The text will exhibit an effect that looks like z-fighting (as seen in the video below, where the [mediaInline] resource pack is used).

Expected behavior

The glowing effect would be rendered behind the text, as was the case prior to 25w09a, and as still happens when a font is loaded from a png file (as seen in the video below, where the [mediaInline] resource pack is used).