Update github checkout action to v2. (#2126)

.github/workflows/ccpp.yml

@@ -21,9 +21,10 @@ jobs:
     - uses: actions/setup-python@v1
       with:
         python-version: ${{ matrix.python-version }}
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
       with:
         submodules: true # 'recursive' 'true' or 'false'
+        persist-credentials: false
     - name: apt dependencies
       if: contains(matrix.os, 'ubuntu')
       run: |