SVG optimization made some icons unreadable

While trying to use some of the SVGs created for buttons on the webpage, I realized the img/buttonIconsBlack/square.svg with following code does not render in Firefox:

https://github.com/flameshot-org/flameshot/blob/236534b17b0318b05b4e28bb906c38c78bae84de/data/img/material/black/square.svg#L1C1-L3C7 :

<svg viewBox="0 0 24 24">
    <path d="M3,3V21H21V3"/>
</svg>

But the same file before the #281 (commit d09580b) with the following content work just fine:

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="24" height="24" viewBox="0 0 24 24"><path d="M3,3V21H21V3" /></svg>

The working icon: , the broken icon:

There are two SVG files in the line above but one of them is rendered in the browser. View page source to confirm.