[BUGFIX] Replace usage of deprecated t3lib_div::testInt().

The statistics module still used that deprecated method.

Fixes: #59651
Releases: 4.0
Change-Id: I529bdb990af73754a8dafae64e0b703e4b6711e6
Reviewed-on: https://review.typo3.org/31689
Reviewed-by: Ivan Dharma Kartolo <ivan.kartolo@gmail.com>
Tested-by: Ivan Dharma Kartolo <ivan.kartolo@gmail.com>