test: fix testSendRequestWithNullRequestId to assert null requestId

The SDK no longer generates a fallback UUID when the server omits
x-request-id; getRequestID() now returns null. Update the assertion
to match the new behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Devesh-Skyflow

src/test/java/com/skyflow/utils/HttpUtilityTests.java

@@ -167,7 +167,7 @@ public void testSendRequestWithNullRequestId() {
             params.addProperty("key", "value");
             String response = httpUtility.sendRequest("GET", url, params, headers);
             Assert.assertEquals(expected, response);
-            Assert.assertNotNull(HttpUtility.getRequestID());
+            Assert.assertNull(HttpUtility.getRequestID());
         } catch (Exception e) {
             fail(INVALID_EXCEPTION_THROWN);
         }