[hotfix] Allow manual triggering of nightly build

Author: MartijnVisser

.github/workflows/weekly.yml

@@ -20,6 +20,7 @@ name: Nightly
 on:
   schedule:
     - cron: "0 0 * * 0"
+  workflow_dispatch:
 jobs:
   compile_and_test:
     if: github.repository_owner == 'apache'