use github action matrix config

Author: Jorrit Poelen

.github/workflows/main.yml

@@ -1,39 +1,17 @@
 name: Java CI
 on: [push]
 jobs:
-  java8:
+  build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [8, 11, 21]
     steps:
       - uses: actions/checkout@v4
       - name: Set up JDK 1.8
         uses: actions/setup-java@v4
         with:
           distribution: 'temurin'
-          java-version: 8
+          java-version: ${{ matrix.java }}
       - name: Test with Maven
         run: mvn test
-  java11:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Set up JDK 11
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'temurin'
-          java-version: 11
-          cache: maven
-      - name: Test with Maven
-        run: mvn test
-  java21:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Set up JDK 21
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'temurin'
-          java-version: 21
-          cache: maven
-      - name: Test with Maven
-        run: mvn test
-