Docs: fix the detailed-0.9 example

[chreekat]

Closes #5124 (in spirit)

Template B: This PR does not modify behaviour or interface

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? [NO] If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[ulysses4ever]

Thanks!

I'm fine with any fix really. I am not sure about comments of this complexity in a little example like this one: the comment now takes a better part of the example... So, I personally would probably just drop the bound. But I understand that different people may disagree on these matters. So, I'm approving as is. Thanks again!

[chreekat]

Tbh I'd just leave off the comment too, but I figured this was the best way to get it merged quickly 😁

[mergify]

This pull request has been removed from the queue for the following reason: pull request branch update failed.

The pull request can't be updated.

You should update or rebase your pull request manually. If you do, this pull request will automatically be requeued once the queue conditions match again.
If you think this was a flaky issue, you can requeue the pull request, without updating it, by posting a @mergifyio requeue comment.