chore: enable CI on PRs

I don't believe we have any secrets, 
should be fine to enable tests on PRs provided by third party contributors.

Author: lidel

.github/workflows/ant.yml

@@ -1,6 +1,6 @@
 name: Java CI
 
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build:
@@ -19,4 +19,4 @@ jobs:
       run: ant -noinput -buildfile build.xml dist
     - name: Run tests
       timeout-minutes: 10
-      run: ant -noinput -buildfile build.xml test
+      run: ant -noinput -buildfile build.xml test