Test multiple SoftHSM versions in GitLab CI
@ondrej suggested that we should be testing multiple SoftHSM
versions in GitLab CI as algorithm support varies:
- SoftHSM < 2.6.0 lacks EdDSA support
- SoftHSM >= 2.6.0 has Ed25519 support
- SoftHSM >= 2.6.1 has Ed448 support