[#9298] Downgrade to Dubbo 2.6.11 due to workflow build failure

[emeroad]

No description provided.

[codecov]

Codecov Report

Merging #9307 (3f3806e) into master (a6850ef) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #9307      +/-   ##
============================================
- Coverage     39.41%   39.39%   -0.02%     
+ Complexity    11775    11774       -1     
============================================
  Files          3407     3407              
  Lines         91260    91260              
  Branches      10118    10118              
============================================
- Hits          35968    35952      -16     
- Misses        52194    52208      +14     
- Partials       3098     3100       +2     

Impacted Files	Coverage Δ
...rp/pinpoint/rpc/packet/ControlHandshakePacket.java	44.82% <0.00%> (-24.14%)	⬇️
...vercorp/pinpoint/rpc/packet/ServerClosePacket.java	47.82% <0.00%> (-17.40%)	⬇️
...m/navercorp/pinpoint/rpc/client/ConnectFuture.java	70.83% <0.00%> (-8.34%)	⬇️
...rp/pinpoint/rpc/server/PinpointServerAcceptor.java	84.10% <0.00%> (-4.64%)	⬇️
...rc/main/java/com/navercorp/pinpoint/test/Item.java	75.92% <0.00%> (+3.70%)	⬆️
...pc/server/LoggingServerMessageListenerFactory.java	90.47% <0.00%> (+9.52%)	⬆️

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