Escape can close multiple windows.
### Default behaviour

By default `sketch` will close a window on a `:keydown` `escape` event:

```lisp
;;; Default events

(defmethod kit.sdl2:keyboard-event :before ((instance sketch) state timestamp repeatp keysym)
  (declare (ignorable timestamp repeatp))
  (when (and (eql state :keydown)
             (sdl2:scancode= (sdl2:scancode-value keysym) :scancode-escape))
    (kit.sdl2:close-window instance)))
```

### Problem

OS: Linux (ubuntu)
SDL version: 2.0.10

Create two windows, move one behind another. Put the mouse to the intersection of two windows.
On `escape` both are closed!

It seems that SDL is sending an extra `:keydown` event for all pressed keys when window regains focus.
When the first window closes, the second one is gaining focus, gets an additional `:keydown` event and closes.

### Relevant discussions

Probably this issue on github is relevant: https://github.com/libsdl-org/SDL/issues/4432

### Solution?

An easy solution could be to move closing to a `:keyup` event, so that there is no additional `:keydown` event for the second window.