services/qingstor: Fix unit test for ListDir

[Xuanwo]

Signed-off-by: Xuanwo github@xuanwo.io

[vercel]

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[codecov]

Codecov Report

Merging #404 into master will increase coverage by 0.06%.
The diff coverage is 76.31%.

@@            Coverage Diff             @@
##           master     #404      +/-   ##
==========================================
+ Coverage   85.47%   85.54%   +0.06%     
==========================================
  Files          12       12              
  Lines         840      844       +4     
==========================================
+ Hits          718      722       +4     
  Misses         74       74              
  Partials       48       48              

Impacted Files	Coverage Δ
services/qingstor/storage.go	74.05% <75.00%> (+0.21%)	⬆️
services/qingstor/utils.go	85.00% <100.00%> (+0.18%)	⬆️

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