Use Java 8 in GitHub Actions workflow

.github/workflows/main.yml

@@ -7,15 +7,15 @@ on:
     branches: [ master ]
 
 jobs:
-  build_and_test:
+  build:
     runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 16
-      uses: actions/setup-java@v1
+    - uses: actions/setup-java@v1
       with:
-        java-version: 16
+        distribution: 'temurin'
+        java-version: 8
 
     - name: Cache maven packages to speed up build
       uses: actions/cache@v1