Docs: Fix misleading `console.log` output example (#41096)
The docs have a misleading `console.log` output for the input
`process.env` that doesn't display all the variables on edge runtime.
The example shows an output of a supposed object with all the
environment variables, but it does this when logging a specific
variable.
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
