test: bump actions/checkout from v1 to v2

PR-URL: #2063
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Christian Clauss <cclauss@me.com>

.github/workflows/Python_tests.yml

@@ -13,7 +13,7 @@ jobs:
         os: [macos-latest, ubuntu-latest, windows-latest]
         python-version: [2.7, 3.6, 3.7, 3.8]  # 3.5,
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v1
         with: