Pixel font renders impossibly small size on tooltips

### Tested versions

4.3 stable

### System information

Linux with X11

### Issue description

When using a pixel font like Terminus, and picking the smallest possible size as Main Font in the settings, some GUI elements still try to render in a smaller font size leading to unreadable text.


(make sure to view the image above at a pixel perfect zoom)

### Steps to reproduce

* use [terminus ttf](https://files.ax86.net/terminus-ttf/) as Main Font and set size to `12`
* check a signal tooltip with args that tries to render at size 10 or something

### Minimal reproduction project (MRP)

no project necessary

Reproduce the issue in Godot 4.3 on Linux with X11 using the Terminus TTF font at size 12, then inspect the signal tooltip UI where arguments are rendered at size 10. Done means tooltip text no longer becomes unreadably smaller than the configured main font size.

Written by the indexing model from the issue text.