avoid wg counter negative

[gaoxinge]

What this PR does:

If we use client.Wait.Done in DataChange in the test, we may encounter the negative watigroup counter negative, because we invoke client.Wait.Add only once at

dubbo-go/remoting/zookeeper/listener_test.go

Line 92 in 1178d9a

client.Wait.Add(1)

but invoke client.Wait.Done twice at

dubbo-go/remoting/zookeeper/listener_test.go

Line 114 in 1178d9a

m.client.Wait.Done()

and

dubbo-go/remoting/zookeeper/client.go

Line 233 in 1178d9a

z.Wait.Done()

So just change client.Wait.Done into client.Close in DataChange, then we can handle this.

[codecov-io]

Codecov Report

Merging #118 into master will decrease coverage by 0.45%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
- Coverage   68.02%   67.56%   -0.46%     
==========================================
  Files          69       69              
  Lines        4350     4350              
==========================================
- Hits         2959     2939      -20     
- Misses       1087     1111      +24     
+ Partials      304      300       -4

Impacted Files	Coverage Δ
cluster/cluster_impl/base_cluster_invoker.go	48.93% <0%> (-19.15%)	⬇️
protocol/dubbo/listener.go	54.58% <0%> (-10.56%)	⬇️
protocol/dubbo/codec.go	68.57% <0%> (-8.58%)	⬇️
protocol/dubbo/readwriter.go	67.56% <0%> (-5.41%)	⬇️
protocol/dubbo/pool.go	56.98% <0%> (-5.03%)	⬇️
remoting/zookeeper/listener.go	48.64% <0%> (+4.86%)	⬆️
remoting/zookeeper/client.go	65.02% <0%> (+5.49%)	⬆️

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[AlexStocks]

@gaoxinge excellent work.