Fix Vercel AI instructions (#13784)

`Sentry.vercelAIIntegration` is not a constructor so drop the `new`
keyword.

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Author: BYK

docs/platforms/javascript/common/configuration/integrations/vercelai.mdx

@@ -37,7 +37,7 @@ The `vercelAIIntegration` adds instrumentation for the [`ai`](https://www.npmjs.
 
 ```javascript
 Sentry.init({
-  integrations: [new Sentry.vercelAIIntegration()],
+  integrations: [Sentry.vercelAIIntegration()],
 });
 ```