doas-related tests should not be limited to OpenBSD systems only

[Fs00]

Describe the bug
doas-related tests (AUTH-9409 and AUTH-9410) are currently performed only on OpenBSD systems.
However, doas is available on several Linux distros (like Gentoo and Arch) thanks to the OpenDoas project, and is even the default choice on Alpine Linux.

Version

• Distribution: Alpine Linux 3.23
• Lynis version: 3.1.6

Expected behavior
Lynis should not skip doas-related tests on Linux systems where doas is installed and configured.

Output (lynis.log)

2025-12-30 13:18:59 ====
2025-12-30 13:18:59 Skipped test AUTH-9409 (Checking /etc/doas.conf file)
2025-12-30 13:18:59 Reason to skip: Incorrect guest OS (OpenBSD only)
2025-12-30 13:18:59 ====
2025-12-30 13:18:59 Skipped test AUTH-9410 (Check /etc/doas.conf file permissions)
2025-12-30 13:18:59 Reason to skip: Incorrect guest OS (OpenBSD only)
2025-12-30 13:18:59 Security check: file is normal
2025-12-30 13:18:59 Checking permissions of /usr/share/lynis/include/tests_kerberos
2025-12-30 13:18:59 File permissions are OK
2025-12-30 13:18:59 ====