Update .env.example file with Vercel deployment suffix

[ga1az]

An environment variable is missing, which is in the middleware, but in the .env.example it does not appear.

  if (
    hostname.includes("---") &&
    hostname.endsWith(`.${process.env.NEXT_PUBLIC_VERCEL_DEPLOYMENT_SUFFIX}`)
  ) {
    hostname = `${hostname.split("---")[0]}.${
      process.env.NEXT_PUBLIC_ROOT_DOMAIN
    }`;
  }

[vercel[bot]]

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