Fix next JSR export

We don't require this because we expect packages to also have ESM exports
declared in their `package.json`, but `next` does not do this, so we must
explicitly use the extension still.

Annoyingly, a dry run publish with `jsr` doesn't reveal this.

packages/inngest/src/next.ts

@@ -21,7 +21,7 @@
  */
 
 import { type NextApiRequest, type NextApiResponse } from "next";
-import { type NextRequest } from "next/server";
+import { type NextRequest } from "next/server.js";
 import {
   InngestCommHandler,
   type ServeHandlerOptions,