[BUGFIX] checkMaximumFileUploadSize shows misleading message

Improve the Install Tool system environment check for
PHP maximum upload size.

Resolves: #58260
Releases: 6.2
Change-Id: I9f0c0694298faa817d9ac827e2f0e7f589cd0611
Reviewed-on: https://review.typo3.org/29696
Reviewed-by: Jost Baron
Tested-by: Jost Baron
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Stefan Neufeind
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters