Update run-tests.yml to use checkout version v3

Author: kmanohar

.github/workflows/run-tests.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v3
       - name: Set up Python 3.7
         uses: actions/setup-python@v1
         with:
@@ -25,7 +25,7 @@ jobs:
         python-version: [3.6, 3.7, 3.8]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v1
       with:
@@ -51,4 +51,4 @@ jobs:
         path: ~/.cache/pip
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements-dev.txt') }}
         restore-keys: |
-          ${{ runner.os }}-pip-
+          ${{ runner.os }}-pip-