Update 400-nextjs-prisma-client-dev-practices.mdx (#5384)

* Update 400-nextjs-prisma-client-dev-practices.mdx

- Add extension to the `db` file as file=./db was a bit misleading
Result: file=./db.ts

* Update content/300-guides/500-other/880-troubleshooting-orm/100-help-articles/400-nextjs-prisma-client-dev-practices.mdx

---------

Co-authored-by: Alex Ruheni <33921841+ruheni@users.noreply.github.com>

content/300-guides/500-other/880-troubleshooting-orm/100-help-articles/400-nextjs-prisma-client-dev-practices.mdx

@@ -20,7 +20,7 @@ In development, the command `next dev` clears Node.js cache on run. This in turn
 
 The solution in this case is to instantiate a single instance `PrismaClient` and save it on the [`globalThis`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis) object. Then we keep a check to only instantiate `PrismaClient` if it's not on the `globalThis` object otherwise use the same instance again if already present to prevent instantiating extra `PrismaClient` instances.
 
-```ts file=./db
+```ts file=db.ts
 import { PrismaClient } from '@prisma/client'
 
 const prismaClientSingleton = () => {