[Authorization] Return if namespace policies are read only (#12514)

* [Authorization Provider] Return early when namespace policies are read only

* Remove typo fix to simplify cherry-picking

(cherry picked from commit f1e72d6)

pulsar-broker-common/src/main/java/org/apache/pulsar/broker/authorization/PulsarAuthorizationProvider.java

@@ -290,6 +290,7 @@ public CompletableFuture<Void> grantPermissionAsync(NamespaceName namespaceName,
             validatePoliciesReadOnlyAccess();
         } catch (Exception e) {
             result.completeExceptionally(e);
+            return result;
         }
 
         ZooKeeper globalZk = configCache.getZooKeeper();