Run primer on latest Python version

Doing so would have caught python#6591

Author: hauntsaninja

.github/workflows/mypy_primer.yml

@@ -26,7 +26,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-python@v2
         with:
-          python-version: 3.8
+          python-version: 3.10
       - name: Install dependencies
         run: pip install git+https://github.com/hauntsaninja/mypy_primer.git
       - name: Run mypy_primer