Fix flaky Network.framework testConnectionFailError test

we may recieve a posix `ECONNREFUSED` too

Author: dnadoba

Tests/AsyncHTTPClientTests/HTTPClientNIOTSTests.swift

@@ -117,7 +117,13 @@ class HTTPClientNIOTSTests: XCTestCase {
         XCTAssertNoThrow(try httpBin.shutdown())
 
         XCTAssertThrowsError(try httpClient.get(url: "http://localhost:\(port)/get").wait()) {
-            XCTAssertEqual($0 as? HTTPClientError, .connectTimeout)
+            if let httpClientError = $0 as? HTTPClientError {
+                XCTAssertEqual(httpClientError, .connectTimeout)
+            } else if let posixError = $0 as? HTTPClient.NWPOSIXError {
+                XCTAssertEqual(posixError.errorCode, .ECONNREFUSED)
+            } else {
+                XCTFail("unexpected error \($0)")
+            }
         }
     }