enhance(play-runner): set allow-modals by default (#634)

fixes #633

Author: LeoMcA

components/play-runner/element.js

@@ -146,6 +146,7 @@ export class MDNPlayRunner extends LitElement {
               "allow-scripts",
               "allow-same-origin",
               "allow-forms",
+              "allow-modals",
               ...(this.sandbox?.split(" ") || []),
             ]),
           ].join(" ")}