prepare release 2.8.0(keep version or will release wrong artifacts)

[liubao68]

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[codecov-commenter]

Codecov Report

Merging #3375 (76cf0e2) into master (17d0efa) will increase coverage by 0.00%.
The diff coverage is 63.63%.

@@            Coverage Diff            @@
##             master    #3375   +/-   ##
=========================================
  Coverage     77.54%   77.54%           
  Complexity     1463     1463           
=========================================
  Files          1650     1650           
  Lines         43799    43806    +7     
  Branches       3685     3687    +2     
=========================================
+ Hits          33963    33971    +8     
+ Misses         8298     8295    -3     
- Partials       1538     1540    +2     

Impacted Files	Coverage Δ
...java/org/apache/servicecomb/it/deploy/Deploys.java	73.64% <63.63%> (-0.82%)	⬇️
...he/servicecomb/foundation/common/net/NetUtils.java	64.80% <0.00%> (-1.61%)	⬇️
...mb/config/ConfigCenterConfigurationSourceImpl.java	10.63% <0.00%> (+1.06%)	⬆️
.../servicecomb/registry/discovery/DiscoveryTree.java	100.00% <0.00%> (+3.50%)	⬆️
...comb/core/definition/MicroserviceVersionsMeta.java	100.00% <0.00%> (+5.26%)	⬆️
...thentication/consumer/RSAConsumerTokenManager.java	77.41% <0.00%> (+6.45%)	⬆️

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