ci: set git fetch-depth to 2 for proper diff comparison

Set fetch-depth to `2` in `actions/checkout` action configuration,
to ensure sufficient git history for file change detection.

The `fetch-depth` option default value is `1`, refer to https://github.com/actions/checkout/blob/v4.2.2/action.yml#L76

Author: huiyifyj

.github/workflows/test.yml

@@ -12,6 +12,8 @@ jobs:
 
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
 
       - name: Install xn bucket
         shell: powershell