Excluded /archives from sitemap if this feature is disabled

[kkomelin]

Description

Currently if SITE.showArchives == false, we still include the /archives page into the XML sitemap, which causes an issue in Google Search Console.

Types of changes

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Documentation Update (if none of the other choices apply)
• Others (any other types not listed above)

Checklist

• I have read the Contributing Guide
• I have added the necessary documentation (if appropriate)
• Breaking Change (fix or feature that would cause existing functionality to not work as expected)

Further comments

Related Issue

Closes: #