Trigger a GitHub build on pull requests.
diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index 90e4a5b..6b4fbd3 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -15,7 +15,7 @@
 
 name: Java CI
 
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build: