Enable workflow dispatch

Author: socheatsok78

.github/workflows/dart.yml

@@ -8,7 +8,8 @@ on:
   schedule:
     # https://crontab.guru/#40_10_*_*_*
     - cron: '40 10 * * *'
-
+  workflow_dispatch:
+  
 jobs:
   test-stable:
     runs-on: ${{ matrix.os }}