data: Rename custom close icon

Resource icons are added to the fallback icon theme, so they won't
get used if a matching icon is found in the configured theme.

That includes fallback names, so Adwaita's "window-close-symbolic"
takes precedence over "window-close-24-symbolic" in hicolor.

Fix this by using a custom name for a custom icon.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1640>

js/ui/windowPreview.js

@@ -353,7 +353,7 @@ var WindowPreview = GObject.registerClass({
         this._closeButton = new St.Button({
             visible: false,
             style_class: 'window-close',
-            child: new St.Icon({ icon_name: 'window-close-24-symbolic' }),
+            child: new St.Icon({ icon_name: 'preview-close-symbolic' }),
         });
         this._closeButton.add_constraint(new Clutter.BindConstraint({
             source: this._windowContainer,