Change Royal Mint, Llantrisant operation date to 1968 [Risolto]

The current mint description says:

Dates of operation 1966-date

Given that the new mint wasn't announced until 1967 that is an unreasonable date to commence operations. The site history on the Royal Mint web site says "the first phase was opened by Her Majesty The Queen on 17 December 1968" so the most optimistic start date would be 1968.

Mint page: https://en.numista.com/catalogue/mint.php?id=16

Source: https://www.royalmint.com/aboutus/50-years-in-llantrisant/

I didn't find any coin pages that specified the Llantrisant location and only issued coins in 1966 or 1967, but there are likely some pages linked to this mint that should also be linked to London.