enable triggering the build on pull requests or manually

Author: aSemy

.github/workflows/build.yml

@@ -1,6 +1,9 @@
 name: Build
 
-on: [ push ]
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
 
 concurrency:
   group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'