grouped-window-list: appGroup - make sure to call PopupMenu.close()

when destroying the hover menu.

When a PopupMenu instance opens, global.menuStackLength is
incremented. Panel tooltips are prevented from showing when
that is non-zero.

When cleaning up after middle-clicking an app, PopupMenu.close()
was not being called, which would decrement that value.

Fixes linuxmint/mint21.2-beta#11

files/usr/share/cinnamon/applets/grouped-window-list@cinnamon.org/menus.js

@@ -1237,7 +1237,7 @@ class AppThumbnailHoverMenu extends PopupMenu.PopupMenu {
         this.willUnmount = true;
         if (!this.box) return;
 
-        if (this.isOpen) this.close();
+        if (this.isOpen) this.close(true);
 
         for (let w = 0, len = this.appThumbnails.length; w < len; w++) {
             if (this.appThumbnails[w] !== undefined) {