message: add test-helpers.js to knownScriptModules
diff: @@ -100,6 +100,7 @@ const legacyJavascriptTypes: ReadonlySet<string|null> = new Set([
  */
  const knownScriptModules = new Set<string>([
  'iron-test-helpers/mock-interactions.js',
  + 'iron-test-helpers/test-helpers.js',
  ]);
  /**
  