test with jdk11 by default

Author: wing328

.github/workflows/samples-kotlin-server.yaml

@@ -59,7 +59,7 @@ jobs:
       - uses: actions/setup-java@v5
         with:
           distribution: 'temurin'
-          java-version: 8
+          java-version: 11
       - name: Cache maven dependencies
         uses: actions/cache@v4
         env: