[TASK] Add tests for ContentObjectRenderer::getData()

* Adds unittests

Change-Id: I2b4ff89c828384c852e6fbf9f82c55e6ebbac281
Resolves: #50258
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/22639
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters