Add final modifier to the class in jetty-httpclient (#11522)

Author: steverao

instrumentation/jetty-httpclient/jetty-httpclient-9.2/library/src/main/java/io/opentelemetry/instrumentation/jetty/httpclient/v9_2/internal/JettyHttpClient9TracingInterceptor.java

@@ -28,7 +28,7 @@
  * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
  * at any time.
  */
-public class JettyHttpClient9TracingInterceptor
+public final class JettyHttpClient9TracingInterceptor
     implements Request.BeginListener,
         Request.FailureListener,
         Response.SuccessListener,