Use helper method to provide helpful error message

What does this MR do and why?

This change uses the expect_allowed and expect_disallowed helper to improve the output of a test failure. Currently, when a test fails it is hard to determine which permission is allowed/disallowed. By using the helper it provides the permission that is causing the failure.

Before:

 Failure/Error: it { is_expected.to be_allowed(*allowed_abilities) }
   expected `#<GroupPolicy (@user10 : Group/456)>.allowed?(:read_dependency, :read_licenses)` to be truthy, got false

After:

 Failure/Error: permissions.each { |p| is_expected.to be_allowed(p) }
   expected `#<GroupPolicy (@user10 : Group/456)>.allowed?(:read_licenses)` to be truthy, got false

This was extracted from !151825 (merged).

#442851 (closed)

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