Upgrade x86 CI machine to Zen 6 when a suitable platform is available

Since we now have AVX-VNNI CI tests, we should have a platform that supports it.
Once a Zen6 miniPC is available to replace our current Zen4 APU then we should do so which will allow it to run in CI.

Additional extensions for testing it would give us:
- AVX-VNNI
- AVX-IFMA
- AVX-NE-CONVERT
- AVX-VNNI-INT8

Explicitly won't give us AVX-VNNI-INT16, but I hear that one is even less interesting anyway.

Start by locating the current Zen4 APU CI machine configuration and the existing AVX-VNNI CI tests. Confirm that a suitable Zen6 miniPC is available, then update the CI host setup to replace the current platform and verify that the listed extensions run in CI.

Written by the indexing model from the issue text.