[BUGFIX] Update extension scanner docs.typo3.org link

The extension scanner docs has recently been moved around
within core api docs. Update the link within the upgrade
module accordingly.

Change-Id: Id74a3fa162db63a4257a1d8d2b6b9037bd661467
Resolves: #83558
Releases: master
Reviewed-on: https://review.typo3.org/55353


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>