fix: tests fail randomly because of KeyGenerator

THe tests fail sometimes, because no explicit key length is given. The
docs specify that there is no guarantee about the exact implementation
on any given platform. Using a specific length is recommended.

src/test/java/org/eclipse/tractusx/managedidentitywallets/config/TestContextInitializer.java

@@ -42,7 +42,10 @@ public class TestContextInitializer implements ApplicationContextInitializer<Con
     public void initialize(ConfigurableApplicationContext applicationContext) {
         KEYCLOAK_CONTAINER.start();
         String authServerUrl = KEYCLOAK_CONTAINER.getAuthServerUrl();
-        SecretKey secretKey = KeyGenerator.getInstance("AES").generateKey();
+        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
+        // use explicit initialization as the platform default might fail
+        keyGen.init(128);
+        SecretKey secretKey = keyGen.generateKey();
         TestPropertyValues.of(
                 "server.port=" + port,
                 "miw.host: localhost:${server.port}",