Update HttpClientExecuteInterceptor.java (#5283)

use the  method httpMethod.setRequestHeader to set the new skywalking headers,so that it can override the exits headers if there is any
Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>

apm-sniffer/apm-sdk-plugin/httpclient-3.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/httpclient/v3/HttpClientExecuteInterceptor.java

@@ -65,7 +65,7 @@ public class HttpClientExecuteInterceptor implements InstanceMethodsAroundInterc
 
         for (CarrierItem next = contextCarrier.items(); next.hasNext(); ) {
             next = next.next();
-            httpMethod.addRequestHeader(next.getHeadKey(), next.getHeadValue());
+            httpMethod.setRequestHeader(next.getHeadKey(), next.getHeadValue());
         }
     }