Fix locations set to None in sitemap

[leocross]

What does this do

Fix a bug with the documentation generating a sitemap with <loc>None</loc> seamingly caused by not having site_url set in the mkdocs config.

e.g.

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>None</loc>
    <lastmod>2023-06-15</lastmod>
    <changefreq>daily</changefreq>
  </url>
  ...
</urlset>

Why is this important

Search engines and other tools use the sitemap, presenting correct information is important for discoverability of the documentation.

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[sonarcloud]

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0 Bugs
0 Vulnerabilities
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