fix yaml syntax of pr builder

Author: willcl-ark

.github/workflows/build.yml

@@ -1,7 +1,7 @@
 # see https://github.com/actions/starter-workflows/blob/main/pages/jekyll.yml for reference
 name: Build
 on:
-  pull-request:
+  pull_request:
     branches: [main, master]
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: