klipper: make "Add Actions" dialog only window-modal

Nate Grahamrequested to merge
work/ngraham/window-modal-add-actions-dialog into master

Reason for the change

Otherwise it blocks all of plasmashell while it's open.

Test plan

  1. Open Klipper settings window > Actions Configuration > Add Action
  2. Click anywhere else in plasmashell, like the panel or the desktop

Bugs fixed

BUG: 501938
FIXED-IN: 6.3.6

Merge request reports