Revert "Disable Xdebug perf optimization when test requires xdebug"

[sebastianbergmann]

Reverts #6353 due to a test that does not fail in the CI pipeline but locally (when Xdebug is loaded):

) /Users/sb/Work/OpenSource/phpunit/tests/end-to-end/regression/6105.phpt Failed asserting that string matches format description. --- Expected +++ Actual @@ @@ Runtime: PHP 8.4.12 Configuration: /Users/sb/Work/OpenSource/phpunit/phpunit.xml -.. 2 / 2 (100%) +.F 2 / 2 (100%) Time: 00:00.048, Memory: 10.00 MB -OK (2 tests, 3 assertions) +There was 1 failure: + +1) IssueTest6105\IssueTest6105::test_case_2_check +Failed asserting that two arrays are identical. +--- Expected ++++ Actual +@@ @@ +-Array &0 [ +- 0 => 'X-Test: Testing', +-] ++Array &0 [] + +/Users/sb/Work/OpenSource/phpunit/src/Framework/Constraint/Constraint.php:105 +/Users/sb/Work/OpenSource/phpunit/src/Framework/Constraint/IsIdentical.php:78 +/Users/sb/Work/OpenSource/phpunit/src/Framework/Assert.php:2573 +/Users/sb/Work/OpenSource/phpunit/src/Framework/Assert.php:1660 +/Users/sb/Work/OpenSource/phpunit/tests/end-to-end/regression/6105/IssueTest6105.php:38 +/Users/sb/Work/OpenSource/phpunit/src/Framework/TestCase.php:1657 +/Users/sb/Work/OpenSource/phpunit/src/Framework/TestCase.php:515 +/Users/sb/Work/OpenSource/phpunit/src/Framework/TestRunner/TestRunner.php:87 +/Users/sb/Work/OpenSource/phpunit/src/Framework/TestCase.php:361 + +FAILURES! +Tests: 2, Assertions: 3, Failures: 1.