ci.yml: Update manifest check git checkout step

Update manifest checkout step to use fetch-depth=0 and fetch the
entire repository history.

.github/workflows/ci.yml

@@ -130,6 +130,7 @@ jobs:
       - uses: actions/checkout@v2
         with:
           submodules: true
+          fetch-depth: 0
       - name: Install Python3
         uses: actions/setup-python@v2
         with: