Add workflow_dispatch event for manifest validation

Author: MaksimZhukov

.github/workflows/validate-manifest.yml

@@ -5,7 +5,7 @@ on:
 # That's one of the reasons we need the schedule to validate the versions-manifest.json file
   schedule:
     - cron: '0 8,20 * * *'
-
+  workflow_dispatch:
   pull_request:
     branches:
       - main