Fix bug in AsyncResponseImpl#register

Fixes: quarkusio#41732

independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/jaxrs/AsyncResponseImpl.java

@@ -153,7 +153,7 @@ public Map<Class<?>, Collection<Class<?>>> register(Class<?> callback, Class<?>.
         Objects.requireNonNull(callback);
         Objects.requireNonNull(callbacks);
         Map<Class<?>, Collection<Class<?>>> ret = new HashMap<>();
-        ret.put(callback.getClass(), register(callback));
+        ret.put(callback, register(callback));
         for (Class<?> cb : callbacks) {
             ret.put(cb, register(cb));
         }