Docs canonical URLs point to pages that return 404 #160

Every page on https://guard-core.github.io/fastapi-guard/ declares a canonical URL that returns 404, for example https://guard-core.github.io/fastapi-guard/latest/<version>/. mike appends the deployed version to site_url (urljoin(site_url, version) in mike/mkdocs_plugin.py), and site_url in mkdocs.yml already ends in /latest/, so the result is /latest/<version>/. Search engines are told the real copy of each page is a URL that does not exist.