[FIX] message-box autogrow

[karlprieb]

@RocketChat/core

Closes #7978

[gdelavald]

There is a small issue when a text line has the right width for the message box, but when the side scroll appears it break the line, causing some flickering on the text by the toggle of line breaks. I'll try and get a recording of this.
Solution might be making it a little bit narrower so the line breaks earlier.
EDIT: Seems like the issue is the toggling between overflow: scroll everytime we update the text.

[karlprieb]

@gdelavald fixed 👍