docs: move misplaced requirement

We don't require VK_KHR_vulkan_memory_model until OpenGL 4.2, so let's
correct that.
3 jobs for !10344 with zink-docs-memmodel in 2 minutes and 26 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Sanity
passed #9033605
sanity

00:00:08

 
  Deploy
passed #9033606
test-docs-mr

00:02:05

 
  Success
passed #9033607
success

00:00:12