Update protect-group-policies.yml

Why is this change being made?

This MR updates the language to change sub-group to subgroup, based on our standards.

https://docs.gitlab.com/ee/development/documentation/styleguide/word_list.html#subgroup

Also, we don't want to say that we allow things, unless we're talking about security. We want to be more active and talk about what the user can do, rather than what we "allow" them to do. https://docs.gitlab.com/ee/development/documentation/styleguide/word_list.html#allow-enable

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