docs: fix vulkan version reported in release notes and related script

Fixes: 4ef3f7e3 ("anv: Enable Vulkan 1.2 support")
Fixes: 7f5462e3 ("radv: enable Vulkan 1.2")
Fixes: 75755e0e ("turnip: Pretend to support Vulkan 1.2")
/cc @dbaker

I'm not sure what the policy should be on fixing older release notes?
On one hand it's a bit late, but on the other at least the website will now report the correct information 🤷