chore: release 2.15.4 [skip ci]

Author: aws-amplify-ops

AmplifyPlugins/Core/AWSPluginsCore/ServiceConfiguration/AmplifyAWSServiceConfiguration.swift

@@ -16,7 +16,7 @@ import Amplify
 public class AmplifyAWSServiceConfiguration {
 
     /// - Tag: AmplifyAWSServiceConfiguration.amplifyVersion
-    public static let amplifyVersion = "2.15.3"
+    public static let amplifyVersion = "2.15.4"
 
     /// - Tag: AmplifyAWSServiceConfiguration.platformName
     public static let platformName = "amplify-swift"