fix: update path for generated prisma client to match the rest of the code

Author: shrekuu

content/800-guides/230-betterauth-nextjs.mdx

@@ -133,7 +133,7 @@ touch src/lib/prisma.ts
 Set up the Prisma client like this:
 
 ```tsx file=src/lib/prisma.ts
-import { PrismaClient } from "@/generated/prisma/client";
+import { PrismaClient } from "@/src/generated/prisma/client";
 import { PrismaPg } from "@prisma/adapter-pg";
 
 const adapter = new PrismaPg({