Update swift-nio to 2.81.0 (#483)

Update swift-nio to 2.81.0 to fix Swift 6 errors

Author: adam-fowler

Package.swift

@@ -17,7 +17,7 @@ let package = Package(
         .library(name: "AWSLambdaTesting", targets: ["AWSLambdaTesting"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-nio.git", from: "2.77.0"),
+        .package(url: "https://github.com/apple/swift-nio.git", from: "2.81.0"),
         .package(url: "https://github.com/apple/swift-log.git", from: "1.5.4"),
     ],
     targets: [