ci: Add Python 3.12

For covering Fedora 41/42, and they may also be added to RHEL 9 at some
point.

3.13 is not yet supported by all Ansible tools:

> py313: failed with env name py313 conflicting with base python python3

So don't add this for now.

Author: martinpitt

.github/workflows/python-unit-test.yml

@@ -27,6 +27,8 @@ jobs:
             os: ubuntu-latest
           - ver: "3.11"
             os: ubuntu-latest
+          - ver: "3.12"
+            os: ubuntu-latest
     runs-on: ${{ matrix.pyver_os.os }}
     steps:
       - name: Update git