02-test_errstr.t: make robust on `openssl errstr` crashes #1988

Job	Run time
check_update	1m 20s
check_docs	56s
check-ansi	2m 28s
address_ub_sanitizer	10m 3s
basic_clang	5m 15s
basic_gcc	4m 56s
fuzz_tests	3m 4s
enable_non-default_options	3m 54s
minimal	2m 20s
no-deprecated	4m 33s
no-shared-macos	6m 51s
non-caching	14m 55s
no-shared-ubuntu	3m 48s
self-hosted (freebsd-13.2)	1s
self-hosted (ubuntu-arm64-22.04)	1s
threads_sanitizer	5m 9s
external-test-cf-quiche	3m 57s
external-test-pyca (1.51.0, 3.9)	7m 34s
external-tests	11m 3s
full_featured	5m 13s
legacy	3m 47s
memory_sanitizer	18m 29s
out-of-readonly-source-and-install-macos	17m 44s
no-legacy	4m 54s
out-of-readonly-source-and-install-ubuntu	6m 38s
	2h 28m 53s

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