fix compilation on macos

Author: sebsto

Tests/AWSLambdaRuntimeTests/LambdaLocalServerTests.swift

@@ -22,6 +22,7 @@ import Testing
 extension LambdaRuntimeTests {
 
     @Test("Local server respects LOCAL_LAMBDA_PORT environment variable")
+    @available(LambdaSwift 2.0, *)
     func testLocalServerCustomPort() async throws {
         let customPort = 8080