chore(dependencies): update actions/checkout action to v3

Author: renovate-bot

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
         python-version: [3.6, 3.7, 3.8, 3.9]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v3
         with: