Use python 3.8 in CI

Author: WillB97

.github/workflows/ci.yml

@@ -10,10 +10,10 @@ jobs:
       MYPY: venv/bin/mypy
     steps:
     - uses: actions/checkout@v3
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v3
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Set up virtualenv
       run: python -m venv venv
     - name: Install dependencies