[github-actions] Run build workflow on pull_request

.github/workflows/build.yml

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0298939..835f5d2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -2,6 +2,7 @@
 
 on:
   push:
+  pull_request:
   schedule:
     - cron: '0 0 1 * *'