ci: add workflow dispatch build action trigger (#391)

currently, if the build test fails in ci, there is no way to retrigger
the test unless commiting to the source branch
this adds the workflow dispatch parameter to allow the job to re-run

.github/workflows/build-snap.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - main
+  workflow_dispatch:
 
 jobs:
   snap: