chore: release 9.0.0+tibiash.6

[tibia-sh-bot]

Releases 9.0.0+tibiash.6. This pull request merges itself once its checks pass. Then the merge commit is tagged v9.0.0+tibiash.6, and the tag publishes the release.

• Read numbers with commas as thousands separators, like 50,000, as the whole number instead of the digits before
  the first comma. This fixes creature hitpoints and experience, item value_buy and value_sell, outfit
  full_price and other quantities. A comma not followed by exactly three digits still ends the number, and an ID list
  like itemid = 629,630,631 or mount_id = 421,437,438,747 still gives its first ID. A creature's max damage
  without a {{Max Damage}} template reads 1,300+ as 1300, and a range like 600-1000? by its larger number.
• Keep the first number of every ID field, like the client IDs, so achievementid = 12,345 gives 12, not 12345. This
  covers house.house_id, achievement.achievement_id, world.world_board, world.trade_board, game_update.news_id
  and item_key.number. No current value changes.
• Add the item.value_buy_currency column. It holds the article's pricecurrency, otherwise a currency written after
  the price in npcprice, like 50 [[Gold Token]]s, otherwise Gold Coin, and NULL when value_buy is NULL or 0.
  A linked currency gives the page it links to, so [[Silver Token]]s gives Silver Token, and mount.price_currency
  now reads links the same way. 25 Years Backpack's price of 7197 is now in Theons, not gold.