Require Java 17 for GH CI

Change-Id: I7de3c00e4f97478dd1205200dfe25010824ca114
diff --git a/.github/workflows/ci_test.yml b/.github/workflows/ci_test.yml
index 26b2a10..68be103 100644
--- a/.github/workflows/ci_test.yml
+++ b/.github/workflows/ci_test.yml
@@ -9,10 +9,10 @@
       - name: Checkout Krill
         uses: actions/checkout@v2
 
-      - name: Set up JDK 11
+      - name: Set up JDK 17
         uses: actions/setup-java@v1
         with:
-          java-version: 11
+          java-version: 17
 
       - name: Build and install Krill
         run: mvn install