Downgrade Python from 3.12 to 3.11

It looks like 3.12 isn't actually available (is only available as prereleases), so try an earlier version of Python, as per the job at https://github.com/arxanas/arxanas.github.io/actions/runs/3527251940/jobs/5916099259.

.github/workflows/main.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: "3.12"
+          python-version: "3.11.0"
 
       - name: Install dependencies
         run: pip install -r requirements.txt