Add workflow_dispatch to our nightly publish script. (#39485)

* Add workflow_dispatch to our nightly publish script.

* Update nightly.yaml

.github/workflows/nightly.yaml

@@ -3,6 +3,8 @@ name: Publish Nightly
 on:
   schedule:
     - cron:  '0 7 * * *'
+  # enable users to manually trigger with workflow_dispatch
+  workflow_dispatch: {}
   repository_dispatch:
     types: publish-nightly