Clear Matter ping result when closing the dialog (#19901)

src/panels/config/integrations/integration-panels/matter/dialog-matter-ping-node.ts

@@ -137,6 +137,7 @@ class DialogMatterPingNode extends LitElement {
   public closeDialog(): void {
     this.device_id = undefined;
     this._status = undefined;
+    this._pingResult = undefined;
     fireEvent(this, "dialog-closed", { dialog: this.localName });
   }