Run unit test with threading mode

The py312-threading tox target will run the currently working unit tests
with threading mode. We have an exclude list, those tests are
failing or hanging. Also the current test list might still have unstable
tests.

This also adds a non voting zuul job to run the new target.

Change-Id: Ibf41fede996fbf2ebaf6ae83df8cfde35acb2b7e
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

.zuul.yaml

@@ -51,6 +51,26 @@
       bindep_profile: test py312
     timeout: 3600
 
+- job:
+    name: nova-tox-py312-threading
+    parent: openstack-tox-py312
+    description: |
+      Run tox-based unit tests for the OpenStack Nova project
+      under cPython version 3.12 with eventlet disabled.
+      Uses tox with the ``py312-threading`` environment.
+
+    required-projects:
+      # including nova here makes this job reusable by other projects and
+      # allow depends-on placement to work with our placement fixture
+      - openstack/nova
+      - openstack/placement
+    vars:
+      # explicitly stating the work dir makes this job reusable by other
+      # projects
+      zuul_work_dir: src/opendev.org/openstack/nova
+      bindep_profile: test py312
+      tox_envlist: py312-threading
+
 - job:
     name: nova-tox-validate-backport
     parent: openstack-tox
@@ -821,6 +841,8 @@
         - barbican-tempest-plugin-simple-crypto:
             irrelevant-files: *nova-base-irrelevant-files
             voting: false
+        - nova-tox-py312-threading:
+            voting: false
     gate:
       jobs:
         - nova-live-migration