tls13secretstest.c: add dummy test function #2031

Job	Run time
basic_gcc	1m 7s
check_docs	48s
check_update	1m 14s
check-ansi	55s
basic_clang	1m 13s
minimal	43s
no-deprecated	1m 3s
no-shared-macos	2m 29s
no-shared-ubuntu	1m 0s
self-hosted (freebsd-13.2)	1s
self-hosted (ubuntu-arm64-22.04)	1s
address_ub_sanitizer	18m 29s
enable_non-default_options	57s
fuzz_tests	2m 58s
memory_sanitizer	26m 19s
non-caching	17m 4s
threads_sanitizer	1m 22s
external-test-cf-quiche	1m 27s
external-test-pyca (1.51.0, 3.9)	1m 20s
full_featured	1m 8s
external-tests	1m 26s
legacy	51s
no-legacy	1m 3s
out-of-readonly-source-and-install-macos	2m 26s
out-of-readonly-source-and-install-ubuntu	1m 0s
	1h 28m 24s

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