change workflow to target the develop branch

.forgejo/workflows/nightly-update.yaml

@@ -9,6 +9,8 @@ jobs:
     steps:
       - name: Check out repository code
         uses: actions/checkout@v4
+        with:
+          ref: develop
       - name: Update flake
         if: ${{ github.event_name == 'schedule' }}
         run: |