Merge pull request #29758 from DaleSeo/patch-4

docs: correct file extension

docs/_snippets/test-runner-custom-page-viewport.md

@@ -29,7 +29,7 @@ module.exports = {
 };
 ```
 
-```ts filename=".storybook/test-runner.js" renderer="common" language="ts"
+```ts filename=".storybook/test-runner.ts" renderer="common" language="ts"
 import type { TestRunnerConfig } from '@storybook/test-runner';
 import { getStoryContext } from '@storybook/test-runner';