fix: the heartbeat task is changed to use scheduleAtFixedRate. (#649)

Co-authored-by: shedfreewu <[email protected]>

Author: shedfreewu

polaris-discovery/polaris-discovery-client/src/main/java/com/tencent/polaris/discovery/client/flow/RegisterFlow.java

@@ -63,7 +63,7 @@ public InstanceRegisterResponse registerInstance(InstanceRegisterRequest request
                 createRegisterV2Header());
         RegisterState registerState = RegisterStateManager.putRegisterState(sdkContext, request);
         if (registerState != null) {
-            registerState.setTaskFuture(asyncRegisterExecutor.scheduleWithFixedDelay(
+            registerState.setTaskFuture(asyncRegisterExecutor.scheduleAtFixedRate(
                     () -> {
                         try {
                             doRunHeartbeat(registerState, registerFunction, heartbeatFunction);