[BUGFIX] Tests: Incomplete mocking of $GLOBALS['TCA'] in ext:frontend

To reduce dependencies of tests and improve readability, some tests
can be improved by better mocking of $GLOBALS['TCA'].

Change-Id: Ib38f2dd94288c5c4f8940d3c8c969ea0459ebbcb
Resolves: #56698
Related: #51436
Releases: 6.2
Reviewed-on: https://review.typo3.org/28204
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters