Only report navigation <link> elements outside of head

[Maxim-Mazurok]

Related to w3c/wcag#2297

The procedure is to

Check that all link elements pertaining to navigation occur in the head section of the document.

But I can see that we're checking all link, regardless of their relation to navigation, including rel="stylesheet" which doesn't make any sense.

HTML_CodeSniffer/Standards/WCAG2AAA/Sniffs/Principle2/Guideline2_4/2_4_8.js

Line 25 in aebdff8

return ['link'];

Please, consider excluding rel="stylesheet" or only including rels related to navigation, like Start, Next, Prev, Contents, Index, etc.