Ignore links to #top when checking anchors

[Lucidiot]

Bug Report

Environment

Zola version: 0.18.0

Expected Behavior

The HTML spec includes some special handling for a #top fragment added to the URL:

10. If decodedFragment is an ASCII case-insensitive match for the string top, then return the top of the document.

This means that adding [some text](#top) to a page correctly creates a link to the top of the page, and Zola should treat the link as always being valid since the anchor is technically always there.

Current Behavior

$ zola check
Checking site...
Checking all internal links with anchors.
> Checked 1 internal link(s) with anchors: 1 target(s) missing.
Failed to check the site
Error: The anchor in the link `@/index.md#top` in /tmp/testsite/content/index.md does not exist.

Steps to reproduce

Add a Markdown link to #top in any page, and run zola check.

Workaround

Linking to # can work instead, as the HTML spec also defines it as an edge case:

3. If fragment is the empty string, then return the special value top of the document.

[Keats]

I didn't know that!