Fix sevlet3 tomcat async test (#12321)

Author: laurit

instrumentation/servlet/servlet-3.0/testing/src/test/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/tomcat/TestServlet3.java

@@ -176,6 +176,11 @@ protected void service(HttpServletRequest req, HttpServletResponse resp) {
               latch.countDown();
             }
           });
+      try {
+        latch.await();
+      } catch (InterruptedException exception) {
+        Thread.currentThread().interrupt();
+      }
     }
   }