Allow manually triggering production deployment

This allows maintainers to optionally update the documentation as PRs are merged
into other Poetry repos rather than needing to wait for the scheduled
deployments.

.github/workflows/deploy-production.yml

@@ -6,6 +6,7 @@ on:
   push:
     branches:
       - main
+  workflow_dispatch: {}
 
 jobs:
   deploy-preview: