Avoid the deprecated URL constructor in the netty observation test

The core modules compile with -Werror, and URL(String) is deprecated as
of Java 20, so the test failed to compile on the JDK 25 build agents and
took the whole build down with it.

Author: gunjansingh-msft

sdk/core/azure-core-http-netty/src/test/java/com/azure/core/http/netty/NettyExpectContinueObservationTests.java

@@ -18,6 +18,7 @@
 import java.io.OutputStream;
 import java.net.ServerSocket;
 import java.net.Socket;
+import java.net.URI;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.util.Locale;
@@ -92,7 +93,7 @@ private static final class ContinueTestServer implements AutoCloseable {
         }
 
         URL url() throws IOException {
-            return new URL("http://localhost:" + serverSocket.getLocalPort() + "/resource");
+            return URI.create("http://localhost:" + serverSocket.getLocalPort() + "/resource").toURL();
         }
 
         void start() {