chore: fix failing Cypress test

Author: ghiscoding

src/app/examples/grid-tree-data-parent-child.component.html

@@ -95,6 +95,7 @@ <h2>
                      [columnDefinitions]="columnDefinitions"
                      [gridOptions]="gridOptions"
                      [dataset]="dataset"
+                     (onGridStateChanged)="handleOnGridStateChanged($event.detail)"
                      (onAngularGridCreated)="angularGridReady($event.detail)"
                      (onBeforeFilterChange)="showSpinner()"
                      (onFilterChanged)="hideSpinner()"