[TASK] Reduce memory usage of a greedy unit test

> Build/Scripts/runTests.sh

Before:
Memory: 469.06 MB

After:
Memory: 373.02 MB

Reason: phpunit executes data providers early and keeps
data sets in memory. The "xml parser big content" tests
create megabytes of data kept in memory. Moving the data
generation from data providers to the test execution
reduces overall memory usage significantly.

Resolves: #104076
Releases: main, 12.4, 11.5
Change-Id: I0ad49824fc1d4c309158b74474853d36af22ffb5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84669


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>