docs: Update deployment.mdx

docs/pages/getting-started/deployment.mdx

@@ -107,6 +107,7 @@ Our example application is also hosted via Docker [here](https://nextjs-docker-e
 
 ```docker filename="Dockerfile"
 # syntax=docker/dockerfile:1
+# syntax=docker/dockerfile:1
 FROM node:20-alpine AS base
 
 # Install dependencies only when needed
@@ -130,9 +131,6 @@ COPY . .
 # Uncomment the following line in case you want to disable telemetry during the build.
 # ENV NEXT_TELEMETRY_DISABLED 1
 
-ARG AUTH_SECRET
-ENV AUTH_SECRET $AUTH_SECRET
-
 RUN corepack enable pnpm && pnpm build
 
 # Production image, copy all the files and run next