cs: Fix PHP-CS-Fixer configuration to exclude `fixtures/bench` #1137

Job	Run time
Lint CS	26s
AutoReview Tests	17s
Unit Tests (PHP 8.2, locked)	26s
Wait for the PHAR & Docker images	5m 37s
Unit Tests (PHP 8.2, lowest)	16s
Unit Tests (PHP 8.2, highest)	18s
Unit Tests (PHP 8.3, highest, --ignore-platform-req=php+)	37s
Update the RequirementChecker	0s
End-to-End Tests (_test_e2e_pass_no_config_min_composer_php, ghcr.io/box-project/box_php725)	19s
End-to-End Tests (_test_e2e_pass_no_config_min_box_php, ghcr.io/box-project/box_php82)	19s
End-to-End Tests (_test_e2e_pass_complete_min_composer_php, ghcr.io/box-project/box_php725)	15s
End-to-End Tests (_test_e2e_pass_complete_min_box_php, ghcr.io/box-project/box_php82)	19s
End-to-End Tests (_test_e2e_fail_complete_min_composer_php, ghcr.io/box-project/box_php725)	16s
End-to-End Tests (_test_e2e_fail_complete_min_box_php, ghcr.io/box-project/box_php82)	17s
End-to-End Tests (_test_e2e_skip_min_composer_php, ghcr.io/box-project/box_php725)	19s
End-to-End Tests (_test_e2e_pass_complete_requirement_checker_not_disabled, ghcr.io/box-project/b...	26s
End-to-End Tests (_test_e2e_fail_conflict, ghcr.io/box-project/box_php82)	19s
RequirementChecker status	1s
	10m 47s

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