Popup windows doesn't stay on the workspace from where they were created

## I'm submitting a…

[x] Bug

[ ] Feature Request

[ ] Documentation Request

[ ] Other (Please describe in detail)

## Current Behavior
When an application on a different workspace creates a new window, this window doesn't stay at the same workspace as the application that created it. Instead it shows up on the active workspace and often steal the input focus for keyboard and mouse.

Given i3 is a tiling WM, even small 100x100px popup windows becomes full screen.

## Expected Behavior
When an application creates a new window it should stay on the workspace as the application that created it.

## Reproduction Instructions
* Put Microsoft Teams in workspace 9
* Switch to workspace 1
* When a meeting is about to start, MS Teams creates a small popup window, that is displayed at workspace 1 instead of workspace 9.

## Environment

Output of `i3 --moreversion 2>&-`:

i3 version: 4.18.2

- Linux Distribution & Version: Fedora 32

- Are you using a compositor (e.g., xcompmgr or compton): No