Add openstack-tox-py312-arm64 job

This seems to have been missed.  I don't know how useful it is, but with
Ubuntu noble shipping with python 3.12 it seems handy.

Change-Id: I7199a7050d4535fcf417d29f73bf7467dd1d64c9

zuul.d/jobs.yaml

@@ -367,6 +367,18 @@
       python_use_pyenv: True
       python_version: '3.12'
 
+- job:
+    name: openstack-tox-py312-arm64
+    parent: openstack-tox-py312
+    nodeset: ubuntu-noble-arm64
+    timeout: 3600
+    description: |
+
+      Run unit tests for an OpenStack Python project under cPython
+      version 3.12 on top of arm64 architecture.
+
+      Uses tox with the ``py312`` environment in arm64 platform.
+
 - job:
     name: openstack-tox-pypy
     parent: openstack-tox