Merge conflict on Panels.PanelWizard when upgrading a subwiki from 9.11.8 to XWiki 10.8.1

STEPS TO REPRODUCE

Preconditions: An older instance of XWiki (e.g. 9.11.8) and an instance of XWiki 10.8.1 (to which will be migrated) are available.

1. Login to the older instance
2. Create a new subwiki
3. Close the instance
4. Go to the newer instance (10.8.1) and copy/cut the

   [...]webapps\xwiki

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

1. Start XWiki and follow the Distribution Wizard through the upgrade process
2. Go to Wiki Index and click on the previously created subwiki name to start the DW

 EXPECTED RESULTS

The upgrade process is completed successfully without errors both on the Main wiki, as well as on subwiki.

 ACTUAL RESULTS

A merge conflict is encountered, related to the page 'Panels.PanelWizard' on Main Wiki's DW as well as on subwiki's DW.

The issue was reproduced on MySQL, PostgreSQL and HSQL.