FIX: Show bulk button on PMs for all users (PR #13801)

canDoBulkActions: reads("currentUser.staff") was added to the bulk button when adding the ability for all users to individually dismiss topics on /new and /unread but it locked out access for non-staff on their PM topic list (/my/messages).

Discussion: I can select messages but no actions appear - bug - Discourse Meta

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@martin-brennan Can you review this? I’m not sure what implications there are when simply passing in true.