Update ci.yml

revert to 3.11 for issues of code conventions which raise warnings in 3.13

Author: nicgowans

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v2
       with:
-        python-version: '3.13'
+        python-version: '3.11'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip