Add workflow dispatch

Author: devlead

.github/workflows/build.yml

@@ -1,5 +1,6 @@
 name: Build
 on:
+  workflow_dispatch:
   pull_request:
   push:
     branches:
@@ -44,4 +45,4 @@ jobs:
       - name: Test Windows
         if: matrix.os == 'windows-latest'
         shell: cmd
-        run: .\test.cmd
+        run: .\test.cmd