fix: add write permissions to update-champions workflow

The workflow failed because the default GITHUB_TOKEN lacked write
access, causing `git push` to return 403.

data/.github/workflows/update-champions.yml

@@ -6,6 +6,9 @@ on:
     - cron: "0 6 * * 4"
   workflow_dispatch:
 
+permissions:
+  contents: write
+
 jobs:
   update:
     runs-on: ubuntu-latest