Update gradle.yml

Author: tomix26

.github/workflows/gradle.yml

@@ -1,5 +1,5 @@
 name: Java CI
-on: push
+on: [push, pull_request]
 jobs:
   build:
     name: Java ${{ matrix.java }}
@@ -24,4 +24,4 @@ jobs:
         restore-keys: |
           ${{ runner.os }}-gradle-
     - name: Build with Gradle
-      run: ./gradlew build
+      run: ./gradlew build