mkeys system test fails intermittently

All recent failures of the "mkeys" system test which popped up in CI were caused by OpenSSL errors in dnssec-keygen:

• https://gitlab.isc.org/isc-projects/bind9/-/jobs/35662
• https://gitlab.isc.org/isc-projects/bind9/-/jobs/36382
• https://gitlab.isc.org/isc-projects/bind9/-/jobs/36546
• https://gitlab.isc.org/isc-projects/bind9/-/jobs/36715

dnssec-keygen: warning: RSA_generate_key_ex failed (crypto failure)
dnssec-keygen: fatal: failed to generate key ./RSASHA1: crypto failure