[fix][test] Deflake TopicPoliciesTest.setupTestTopic by retrying forced namespace deletion (#25974)

Author: lhotari

pulsar-broker/src/test/java/org/apache/pulsar/broker/admin/TopicPoliciesTest.java

@@ -175,16 +175,11 @@ void setupTestTopic() throws Exception {
         } catch (PulsarAdminException.NotFoundException e) {
             // topic may already be deleted
         }
-        try {
-            admin.namespaces().deleteNamespace(myNamespace, true);
-        } catch (PulsarAdminException.NotFoundException e) {
-            // namespace may already be deleted
-        }
-        try {
-            admin.namespaces().deleteNamespace(myNamespaceV1, true);
-        } catch (PulsarAdminException.NotFoundException e) {
-            // namespace may already be deleted
-        }
+        // Use deleteNamespaceWithRetry since the forced namespace deletion can fail transiently with HTTP 422 when a
+        // topic deletion in the cascade races with concurrent topic loading; the helper retries and treats an
+        // already-deleted namespace as success.
+        deleteNamespaceWithRetry(myNamespace, true);
+        deleteNamespaceWithRetry(myNamespaceV1, true);
         admin.namespaces().createNamespace(testTenant + "/" + testNamespace, Set.of("test"));
         admin.namespaces().createNamespace(myNamespaceV1);
         admin.topics().createPartitionedTopic(testTopic, testTopicPartitions);