Fix the changelog script on GitHub Actions

actions/checkout doesn’t fetch full history by default, but the changelog script needs it. This one-liner fixes the issue.

Issue: #266

Author: mathiasbynens

.github/workflows/update.yml

@@ -15,6 +15,8 @@ jobs:
         with:
           ref: ${{ github.head_ref }}
           token: ${{ secrets.PERSONAL_ACCESS_TOKEN }}
+          # Fetching full history is required for the changelog script.
+          fetch-depth: 0
 
       - name: Set up Node.js
         uses: actions/setup-node@v3