test/bioprinttest.c: use the whole buffer for checks

test/bioprinttest.c: use the whole buffer for checks

There is no need to decrement the size of buffer by 1, snprintf should
terminate the output with a \0.

Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28177)