gha: add workflow_dispatch

Author: lazka

.github/workflows/build.yml

@@ -1,6 +1,9 @@
+name: 'build'
+
 on:
   push:
   pull_request:
+  workflow_dispatch:
   schedule:
     - cron: '0 0 * * 0'
 
@@ -51,4 +54,4 @@ jobs:
           token: ${{ secrets.GITHUB_TOKEN }}
           tag: nightly-x86_64
           rm: true
-          files: msys2-*
+          files: msys2-*