add tests for priority

[bookstack] / dev / api / requests / chapters-update.json

{
  "book_id": 1,
  "name": "My fantastic updated chapter",
  "description": "This is an updated chapter that I've altered via the API",
  "tags": [
    {"name": "Category", "value": "Kinda Good Content"},
    {"name": "Rating", "value": "Medium"}
  ],
  "priority": 15
}