build: build docs with Python3.11

This makes type hints flow through more nicely because of changes made by ruff.

.github/workflows/ci.yaml

@@ -23,13 +23,13 @@ jobs:
         id: setup-python
         uses: actions/setup-python@v4
         with:
-          python-version: "3.9"
+          python-version: "3.11"
       - name: Load cached Poetry installation
         id: cached-poetry
         uses: actions/cache@v3
         with:
           path: ~/.local  # the path depends on the OS
-          key: poetry-1  # increment to reset cache
+          key: poetry-2  # increment to reset cache
       - name: Install Poetry
         if: steps.cached-poetry.outputs.cache-hit != 'true'
         uses: snok/install-poetry@v1
@@ -38,7 +38,7 @@ jobs:
         uses: actions/cache@v3
         with:
           path: .venv
-          key: venv-linting-${{ hashFiles('**/poetry.lock') }}
+          key: venv-linting-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('**/poetry.lock') }}
       - name: Install dependencies
         run: |
           poetry config virtualenvs.create true

.readthedocs.yaml

@@ -11,7 +11,7 @@ version: 2
 build:
   os: ubuntu-22.04
   tools:
-    python: "3.9"
+    python: "3.11"
   jobs:
     post_create_environment:
       - pip install poetry