Normcap not shown in fullscreen when using gnome-shell and PopOS tiling

[dynobo]

The windows with the red border showing the screenshots to select a region are not covering the full screen, but are getting tiled by the window manager. This is at least the case on Ubuntu 20.04 with the gnome-shell extension of PopOS.

Tasks:

• Test some different window managers to see where else this issue occurs
• Try setting self.tk.attributes("-zoomed", True) for linux
• Think about if it's possible to write a unit test for this issue

[dynobo]

Should be fixed with e11cc1c