CMP app: fix combination of -certout and -chainout with equal filename arg #25535

Job	Run time
basic_gcc	7m 11s
address_ub_sanitizer	11m 58s
basic_clang	6m 34s
check_docs	1m 1s
check_update	1m 17s
check-ansi	2m 31s
minimal	2m 41s
no-deprecated	6m 19s
non-caching	17m 23s
no-shared-macos (macos-13)	6m 24s
no-shared-ubuntu	5m 7s
no-shared-macos (macos-14)	5m 42s
self-hosted (freebsd-13.2)	14m 33s
self-hosted (ubuntu-arm64-22.04)	31m 27s
enable_non-default_options	4m 49s
external-test-cf-quiche	3m 52s
external-test-pyca (1.51.0, 3.9)	6m 48s
external-tests	11m 18s
full_featured	7m 2s
fuzz_tests	2m 59s
legacy	5m 19s
memory_sanitizer	19m 26s
no-legacy	7m 21s
out-of-readonly-source-and-install-macos (macos-13)	11m 51s
out-of-readonly-source-and-install-ubuntu	7m 48s
out-of-readonly-source-and-install-macos (macos-14)	6m 40s
threads_sanitizer	7m 18s
	3h 42m 39s

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