Update typo in AWS Secrets Engine documentation (hashicorp#28930)

Co-authored-by: Kuba Wieczorek <[email protected]>

website/content/docs/secrets/aws.mdx

@@ -14,7 +14,7 @@ involve clicking in the web UI. Additionally, the process is codified and mapped
 to internal auth methods (such as LDAP). The AWS IAM credentials are time-based
 and are automatically revoked when the Vault lease expires.
 
-Vault supports three different types of credentials to retrieve from AWS:
+Vault supports four different types of credentials to retrieve from AWS:
 
 1. `iam_user`: Vault will create an IAM user for each lease, attach the managed
    and inline IAM policies as specified in the role to the user, and if a