fix issue-8516 on 2.6.x: fix mock:true configuration

[changfubai]

fix #8516 on branch 2.6.x.
ps: this commit has been merge into 3.0 and master branch.

[codecov-commenter]

Codecov Report

Merging #8623 (35fed07) into 2.6.x (f62ca3f) will increase coverage by 0.34%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##              2.6.x    #8623      +/-   ##
============================================
+ Coverage     47.04%   47.39%   +0.34%     
- Complexity     4472     4519      +47     
============================================
  Files           577      577              
  Lines         25631    25632       +1     
  Branches       4546     4547       +1     
============================================
+ Hits          12059    12148      +89     
+ Misses        11710    11602     -108     
- Partials       1862     1882      +20     

Impacted Files	Coverage Δ
...ava/com/alibaba/dubbo/rpc/support/MockInvoker.java	57.40% <66.66%> (+57.40%)	⬆️
...aba/dubbo/remoting/transport/mina/MinaChannel.java	42.25% <0.00%> (-11.27%)	⬇️
.../com/alibaba/dubbo/monitor/dubbo/DubboMonitor.java	87.85% <0.00%> (-1.87%)	⬇️
...baba/dubbo/remoting/transport/mina/MinaClient.java	58.46% <0.00%> (+1.53%)	⬆️
.../alibaba/dubbo/rpc/proxy/AbstractProxyFactory.java	4.76% <0.00%> (+4.76%)	⬆️
...om/alibaba/dubbo/rpc/filter/ActiveLimitFilter.java	88.88% <0.00%> (+5.55%)	⬆️
...n/java/com/alibaba/dubbo/rpc/support/RpcUtils.java	27.02% <0.00%> (+6.75%)	⬆️
...src/main/java/com/alibaba/dubbo/rpc/RpcResult.java	46.15% <0.00%> (+7.69%)	⬆️
...main/java/com/alibaba/dubbo/rpc/RpcInvocation.java	25.55% <0.00%> (+10.00%)	⬆️
...bbo/rpc/proxy/wrapper/StubProxyFactoryWrapper.java	18.42% <0.00%> (+18.42%)	⬆️
... and 3 more

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