Sortable: Use an event object for simulated `mouseup` in `cancel()`

Regression caused by a1d6920

Fixes #15042
Closes gh-1746

ui/widgets/sortable.js

@@ -518,7 +518,7 @@ return $.widget( "ui.sortable", $.ui.mouse, {

		if ( this.dragging ) {

			this._mouseUp( { target: null } );
			this._mouseUp( new $.Event( "mouseup", { target: null } ) );

			if ( this.options.helper === "original" ) {
				this.currentItem.css( this._storedCSS );