JACOCO-66 Build and run unit tests with Java 21

Author: dorian-burihabwa-sonarsource

build.gradle

@@ -21,6 +21,12 @@ if (version.endsWith('-SNAPSHOT') && ext.buildNumber != null) {
     version = version.replace('-SNAPSHOT', versionSuffix)
 }
 
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
 compileJava {
     // Setting the compatibility to Java 17
     options.release = 17

mise.toml

@@ -1,3 +1,3 @@
 [tools]
-java = "17.0"
+java = "21"
 gradle = "9.2"