Update...

Update apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/context/trace/AbstractTracingSpan.java

Fix isInAsyncMode never be set.
Co-Authored-By: wu-sheng <wu.sheng@foxmail.com>

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/context/trace/AbstractTracingSpan.java

@@ -323,6 +323,7 @@ public abstract class AbstractTracingSpan implements AbstractSpan {
 
     @Override public AbstractSpan prepareForAsync() {
         context = ContextManager.awaitFinishAsync(this);
+        isInAsyncMode = true;
         return this;
     }