Important: #89269 - Introduce Upgrade Wizard for invalid Backend User configuration

See forge#89269


Each database record in table be_users stores an individual user configuration in the field uc. It is exposed during runtime in $GLOBALS['BE_USER']->uc.

In older TYPO3 versions serialized class instances of \stdClass have been persisted to mentioned field - which is not possible anymore since TYPO3 v9.

A corresponding upgrade wizard "Update backend user configuration array" aims to convert \stdClass data to plain PHP arrays using scalar values.

Since this upgrade wizard was introduced late with TYPO3 v9.5.11 it is suggested to make sure this upgrade step is executed in case a website has been updated before (e.g. from TYPO3 v8 to TYPO3 v9.5.1).