Adjust fetch depth

v4 of the checkout action changes the way branches are handled. Including this arg ensures that the scrapy validate step doesn't fail when it attempts to. checkout the "main" branch. Without this arg, the workflow can't find the "main" branch.

.github/workflows/ci.yml

@@ -19,6 +19,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5