Run CI on both Java 11 and 17.

.github/workflows/ci.yml

@@ -9,14 +9,17 @@ on:
 jobs:
   build-and-test:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [11, 17]
     steps:
       - uses: actions/checkout@v2.3.5
 
-      - name: set up JDK 11
+      - name: set up JDK ${{ matrix.java }}
         uses: actions/setup-java@v2
         with:
-          java-version: 11
-          distribution: 'adopt-openj9'
+          java-version: ${{ matrix.java }}
+          distribution: temurin
           check-latest: true
 
       - name: Cache Gradle dependencies