Update ticket information for last call sale

docs/tickets.md

 # Tickets
 
-The presale is over, and all tickets have been sold.
+There are still a few tickets available: [blogpost](https://events.ccc.de/2023/07/10/last-call-presale/).
 
 If you need to look up your order, you can find the ticket shop here: <https://tickets.events.ccc.de/>.
 
-The merch presale is also over. Some additional merch will be sold at the event.
+The merch presale is over. Some additional merch will be sold at the event.
 
 ## Prices