Update main.yml

.github/workflows/main.yml

-name: CI
+name: Gradle CI
 
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build:
@@ -8,7 +8,12 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v1
-      - name: setup-android
-        run: chmod 777 gradlew & ./gradlew build -x mirai-core:jvmTest
-
+    - uses: actions/checkout@v2
+    - name: Set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Grant execute permission for gradlew
+      run: chmod +x gradlew
+    - name: Build with Gradle
+      run: ./gradlew build