Empty revision is added in the history for pages with comments when upgrading from certain XWiki versions

STEPS TO REPRODUCE

1. Open an instance of XWiki 8.4.6
2. Add a comment to a page (created or already existing, e.g. Sandbox)
3. Close the instance
4. Go to a newer instance (tested with 12.10.8 and 13.5) and copy/cut the

   [...]webapps\xwiki

   folder and replace it (first delete the old one) in the same location on the older (8.4.6) version

1. Start XWiki and finish running the DW for upgrade
2. Go to the page where the comment was added, access History tab

EXPECTED RESULTS

The most recent page revision displayed is when the (last) comment was added (saved at the respective date and time).

ACTUAL RESULTS

There is an additional empty page revision saved at the time of the upgrade and which is displayed as the current version, having as summary:

Migrated property [author] from class [XWiki.XWikiComments]

The issue was reproduced also when performing an upgrade from XWiki 9.11.8 to 12.10.8 or 13.5; however, it didn't reproduce when upgrading from XWiki 10.11.11.

The issue can be very important for wikis with a large volume of content, since it alters last modification dates of documents.

The issue was initially discovered by lucaa.