Fix Private Messages self-quoting private posts being changed to followers-only (#36249)

spec/services/post_status_service_spec.rb

@@ -321,6 +321,14 @@ RSpec.describe PostStatusService do
     expect(status).to be_private_visibility
   end
 
+  it 'correctly preserves visibility for private mentions self-quoting private posts' do
+    account = Fabricate(:account)
+    quoted_status = Fabricate(:status, account: account, visibility: :private)
+
+    status = subject.call(account, text: 'test', quoted_status: quoted_status, visibility: 'direct')
+    expect(status).to be_direct_visibility
+  end
+
   it 'returns existing status when used twice with idempotency key' do
     account = Fabricate(:account)
     status1 = subject.call(account, text: 'test', idempotency: 'meepmeep')