(maint) Expands test to include macOS 12

This test excludes all versions of macOS starting from 10.15
Catalina. As Puppet dropped macOS 10.14 Mojave support last year,
we no longer have to use a regex matcher as every supported
version of macOS can be excluded.

Author: mhashizume

acceptance/tests/resource/file/ticket_8740_should_not_enumerate_root_directory.rb

@@ -1,7 +1,7 @@
 test_name "#8740: should not enumerate root directory"
 
 confine :except, :platform => 'windows'
-confine :except, :platform => /(osx-10.1[5-9]|osx-11-)/
+confine :except, :platform => 'osx'
 
 tag 'audit:high',
     'audit:refactor',   # Use block style `test_name`