[BUGFIX] Use correct `DateInterval` objects in `RotatingFileWriterTest`

The `RotatingFileWriterTest` previously used a timestamp-based
calculation to mock file names. This approach conflicts with the
`DateInterval`-based calculation and might lead to false-negative test
results. This commit updates the test cases by using the interval-based
calculation now.

Resolves: #103243
Releases: main
Change-Id: I9b08b797377eb504af7707acf520fae896b6cbb1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83177


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>