Clicking on the editor border triggers file upload dialog

How to reproduce

1. Open any page that has a markdown (plain) text editor
2. Click the area between editor border and text input (text cursor will be a pointer, the area is 1-3 pixels wide)
3. A file upload dialog will pop up

Video demonstration

Screen_Recording_2023-11-01_at_20.11.35

Implementation Guide

Replace the margin with padding (see #430108 (comment 1630244255))