Update tox CI Python version to 3.12

Author: Alex-Welsh

.github/workflows/stackhpc-pull-request.yml

@@ -40,11 +40,11 @@ jobs:
       matrix:
         include:
           - environment: pep8
-            python-version: "3.10"
+            python-version: "3.12"
           - environment: releasenotes
-            python-version: "3.10"
+            python-version: "3.12"
           - environment: docs
-            python-version: "3.10"
+            python-version: "3.12"
     name: Tox ${{ matrix.environment }} with Python ${{ matrix.python-version }}
     if: github.repository == 'stackhpc/stackhpc-kayobe-config'
     steps: