[TASK] Re-add unit tests for ExtensionCompatibilityTester

The tests for the ExtensionCompatibilityTester are currently skipped.
This patch removes the broken tests and leaves the working ones.

Releases: 6.3, 6.2
Resolves: #59700
Change-Id: I10a49d0dddf2807bd50944837e31f0105374c8c9
Reviewed-on: https://review.typo3.org/31370
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn