[BUGFIX] Fix typo in sys_registry key for fetching last wizard position

This fix will let upgrade wizard "Execute database migrations on single rows" restore
last reached position whenever the wizard is run again.

Change-Id: Iccaa14f82db4501447e7c553498a36074898b85b
Resolves: #81066
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/52651


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>