update comment for "dynamic" field

[liujunzxcv]

No description provided.

[codecov-io]

Codecov Report

Merging #3900 into master will decrease coverage by 0.09%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master    #3900     +/-   ##
===========================================
- Coverage     63.73%   63.63%   -0.1%     
  Complexity       71       71             
===========================================
  Files           712      712             
  Lines         31450    31450             
  Branches       5073     5073             
===========================================
- Hits          20044    20014     -30     
- Misses         9113     9140     +27     
- Partials       2293     2296      +3

Impacted Files	Coverage Δ	Complexity Δ
...org/apache/dubbo/config/AbstractServiceConfig.java	100% <ø> (ø)	0 <0> (ø)	⬇️
...ache/dubbo/remoting/p2p/support/AbstractGroup.java	45.45% <0%> (-11.37%)	0% <0%> (ø)
.../remoting/transport/netty4/NettyServerHandler.java	61.9% <0%> (-9.53%)	0% <0%> (ø)
...ng/transport/dispatcher/all/AllChannelHandler.java	51.42% <0%> (-5.72%)	0% <0%> (ø)
...ng/exchange/support/header/HeartbeatTimerTask.java	73.68% <0%> (-5.27%)	0% <0%> (ø)
.../org/apache/dubbo/remoting/ExecutionException.java	15.78% <0%> (-5.27%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (-4.35%)	0% <0%> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	77.77% <0%> (-2.69%)	0% <0%> (ø)
...exchange/support/header/HeaderExchangeHandler.java	59.84% <0%> (-2.37%)	0% <0%> (ø)
...he/dubbo/registry/multicast/MulticastRegistry.java	67.87% <0%> (-1.81%)	0% <0%> (ø)
... and 1 more

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[carryxyh]

Hi, thx for your pr.