CI: upgrade to python 3.12

HA is now deefaulting to 3.12, so follow step.

.github/workflows/linting.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v4
         with:
-          python-version: '3.11'
+          python-version: '3.12'
 
       - name: Install dependencies
         run: |

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.11']
+        python-version: ['3.12']
 
     steps:
       - uses: actions/checkout@v3