add skip when aws key is null (opensearch-project#2926) (opensearch-project#2928)

Signed-off-by: Mingshi Liu <mingshl@amazon.com>
(cherry picked from commit 93d0429)

Co-authored-by: Mingshi Liu <mingshl@amazon.com>

Author: opensearch-trigger-bot[bot]

plugin/src/test/java/org/opensearch/ml/rest/RestMLInferenceSearchResponseProcessorIT.java

@@ -257,6 +257,10 @@ public void testMLInferenceProcessorRemoteModelCustomPrompt() throws Exception {
      * @throws Exception if any error occurs during the test
      */
     public void testMLInferenceProcessorRemoteModelStringField() throws Exception {
+        // Skip test if key is null
+        if (AWS_ACCESS_KEY_ID == null) {
+            return;
+        }
         String createPipelineRequestBody = "{\n"
             + "  \"response_processors\": [\n"
             + "    {\n"