ci: use JDK 11 but compile for 8

Author: quintesse

.github/workflows/ci.yml

@@ -22,10 +22,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 8
+    - name: Set up JDK 11
       uses: actions/setup-java@v4
       with:
-        java-version: '8'
+        java-version: '11'
         distribution: 'temurin'
         cache: maven
     - name: Build with Maven