[7.17] Upgrade actions/checkout to v2

Author: sethmlarson

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Set up Python 3.7
         uses: actions/setup-python@v2
         with:
@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Set up Python 3.7
         uses: actions/setup-python@v2
         with:
@@ -49,7 +49,7 @@ jobs:
     continue-on-error: ${{ matrix.experimental }}
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Set Up Python - ${{ matrix.python-version }}
         uses: actions/setup-python@v2
         with: