Self-reference detection fails if `prettyurls = false`

References to the (same) enclosing docstring itself aren't usually linked. However, this self-reference detection does not seem to work if the page is generated with `format = Documenter.HTML(prettyurls = false)`:

**MWE** (`Pkg.generate`d package with documented `greet()` function and minimal documenter setup)

- `prettyurls = true`

- `prettyurls = false`

[SomePackage.zip](https://github.com/user-attachments/files/31645215/SomePackage.zip)

Start with the minimal Documenter setup and the attached SomePackage.zip, comparing generated output with Documenter.HTML(prettyurls = true) and prettyurls = false. Trace self-reference detection for the documented greet() function; done means the same enclosing docstring is not incorrectly linked in both output modes.

Written by the indexing model from the issue text.