TEMP: Add manual workflow_dispatch

.github/workflows/build.yml

@@ -2,10 +2,7 @@
 # For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
 
 name: build
-on:
-  push:
-    branches:
-      - master
+on: ["push", "pull_request", "workflow_dispatch"]
 jobs:
   manylinux:
     runs-on: ubuntu-18.04