test(system.rb): add support for `mac_os_x` [skip ci]

* Automated using https://github.com/myii/ssf-formula/pull/442

test/integration/share/inspec.yml

   - platform-name: gentoo
   - platform-name: almalinux
   - platform-name: rocky
+  - platform-name: mac_os_x
   - platform: windows

test/integration/share/libraries/system.rb

       'base-latest'
     when 'gentoo'
       "#{inspec.platform[:release].split('.')[0]}-#{derive_gentoo_init_system}"
+    when 'mac_os_x'
+      inspec.command('sw_vers -productVersion').stdout.to_s
     when 'opensuse'
       # rubocop:disable Style/NumericLiterals,Layout/LineLength
       inspec.platform[:release].to_i > 20210101 ? 'tumbleweed' : inspec.platform[:release]