[BUGFIX] Extbase container injection test triggers PHP bug

PHP's reflection behaves differently in an edge case used in
extbase constructor injection.
The patch removes the specific check from tests and adds
documentation of this case.

Change-Id: I8ff5ce0d87a28f93ae6be0fd5778289cc9cab7aa
Resolves: #55538
Related: #52349
Releases: 6.2
Reviewed-on: https://review.typo3.org/27219
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn