fix: check that root element exists in ts plugin template (#2385)

* fix: Use non-null assertion operator for `root` to pass type check

* chore: Remove non-null assertion operator

* chore: format code

Author: jschanker

plugins/dev-create/templates/typescript-plugin/template/test/index.ts

@@ -36,9 +36,9 @@ document.addEventListener('DOMContentLoaded', function () {
   const defaultOptions = {
     toolbox: toolboxCategories,
   };
-  createPlayground(
-    document.getElementById('root'),
-    createWorkspace,
-    defaultOptions,
-  );
+  const rootElement = document.getElementById('root');
+  if (!rootElement) {
+    throw new Error(`div with id 'root' not found`);
+  }
+  createPlayground(rootElement, createWorkspace, defaultOptions);
 });