Update Build_Release.yml

.github/workflows/Build_Release.yml

@@ -31,6 +31,8 @@ jobs:
       - name: Test with pytest
         run: |
             pytest PyCTBN/tests/>
+      - name: Checkout code
+            uses: actions/checkout@v2
       - name: Install dependencies
         run: |
             python -m pip install --upgrade pip