DOCSP-32565: Fix the AWS refresh credentials example (mongodb#430)

Author: Chris Cho

source/fundamentals/auth.txt

@@ -489,7 +489,7 @@ that returns new credentials as shown in the following example:
    :dedent:
    :start-after: start refreshCredentials
    :end-before: end refreshCredentials
-   :emphasize-lines: 4-5,9
+   :emphasize-lines: 4-5,8-9
 
 .. note::
 

source/includes/fundamentals/code-snippets/MongoDbAwsAuth.java

@@ -108,7 +108,7 @@ private static void refreshCredentials() {
             return new AwsCredential("<awsKeyId>", "<awsSecretKey>", "<awsSessionToken>");
         };
 
-        MongoCredential credential = MongoCredential.createAwsCredential("<awsKeyId>", "<awsSecretKey>".toCharArray())
+        MongoCredential credential = MongoCredential.createAwsCredential(null, null)
                 .withMechanismProperty(MongoCredential.AWS_CREDENTIAL_PROVIDER_KEY, awsFreshCredentialSupplier);
         MongoClient mongoClient = MongoClients.create(
                 MongoClientSettings.builder()