chore: Upgrade to Java 21 (#53)

Author: Oliver Weiler

.github/workflows/ci.yml

@@ -21,10 +21,10 @@ jobs:
       - name: Set up Java
         uses: actions/setup-java@v3
         with:
-          distribution: temurin
+          distribution: zulu
           java-version: |
             8
-            17
+            21
           cache: maven
       - name: Cache Sonar
         uses: actions/cache@v3

pom.xml

@@ -33,7 +33,7 @@
 
     <properties>
         <java.version>8</java.version>
-        <java.testVersion>17</java.testVersion>
+        <java.testVersion>21</java.testVersion>
         <maven.compiler.source>${java.version}</maven.compiler.source>
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <maven.compiler.testRelease>${java.testVersion}</maven.compiler.testRelease>