openstack-charms: align to Ubuntu Pythons

We've managed to end up with a mix of Python version targets for
each branch of the repositories under the OpenStack Charms project.

Python testing runtimes should be aligned to the Python base version
shipped in the Ubuntu releases each charm branch needs to support.

Re-align the main template job used for stable/2023.1 onwards with
this; this reduces the amount of test resources the projects reviews
with consume.

For the master branch (which will target Ubuntu 24.04 LTS) make the
test for Python 3.12 voting.

Change-Id: Idba042028c8100246d78c31746dd1aff98ed88f3

zuul.d/project-templates.yaml

@@ -622,66 +622,44 @@
 
 - project-template:
     name: openstack-python3-charm-jobs
-    # NOTE(gmann): We are using this generic template for python version
-    # testing. When a new development cycle starts, we need to do two things:
-    # 1. Update this template for the python version jobs as per the
-    #    new development cycle tetsing runtime defined by TC
-    #    https://governance.openstack.org/tc/reference/runtimes/
-    #    Use the 'branches' variant to run the applicable python version
-    #    jobs.
-    # 2. Make sure the previous cycle applicable jobs continue to run for
-    #    the new stable branch. Use the 'branches' variant to run the
-    #    applicable python version jobs.
+    # NOTE(coreycb,jamespage): This template is used in OpenStack Charms since
+    # stable/2023.1.  Charm unit tests should be aligned to the Python version
+    # found in the Ubuntu releases they support.
     #
-    # NOTE(coreycb): This template is used in openstack charms since
-    # stable/2023.1. While the stable/2023.1 and stable/2023.2 charm branches
-    # should support py311 unit tests, they do not. They need to continue
-    # supporting py310.
+    #   Ubuntu 20.04 LTS - Python 3.8
+    #   Ubuntu 22.04 LTS - Python 3.10
+    #   Ubuntu 24.04 LTS - Python 3.12
+    #
+    # As this template is only used from stable/2023.1 onwards, the minimum
+    # Python version this template needs to support is Python 3.10 as early
+    # releases of the charms are configured directly in each repository.
+    #
+    # This template should *not* be updated in-line with the agreed testing
+    # runtimes for the rest of the OpenStack projects.
     description: |
       Runs unit tests for an OpenStack Charm project under the CPython
       version 3 releases designated for testing the latest release.
     check:
       jobs:
         - openstack-tox-pep8
-        - openstack-tox-py38:
-            branches:
-              - stable/2023.1
-              - stable/2023.2
-              - stable/2024.1
-        - openstack-tox-py39:
-            branches:
-              - master
         - openstack-tox-py310:
             branches:
               - stable/2023.1
               - stable/2023.2
-        - openstack-tox-py311:
-            branches:
               - stable/2024.1
-              - master
-        # py3.12 testing is added as non voting from 2024.2 release onwards.
         - openstack-tox-py312:
             branches:
               - master
-            voting: false
     gate:
       jobs:
         - openstack-tox-pep8
-        - openstack-tox-py38:
-            branches:
-              - stable/2023.1
-              - stable/2023.2
-              - stable/2024.1
-        - openstack-tox-py39:
-            branches:
-              - master
         - openstack-tox-py310:
             branches:
               - stable/2023.1
               - stable/2023.2
-        - openstack-tox-py311:
-            branches:
               - stable/2024.1
+        - openstack-tox-py312:
+            branches:
               - master
 
 - project-template: