Fix the wrong return value of onnx similarity evaluation

[SimFG]

issue: #459 #386

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[codecov]

Codecov Report

Merging #460 (234662d) into dev (de35ae6) will decrease coverage by 0.03%.
The diff coverage is 83.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #460      +/-   ##
==========================================
- Coverage   94.02%   93.99%   -0.03%     
==========================================
  Files          92       92              
  Lines        3583     3583              
==========================================
- Hits         3369     3368       -1     
- Misses        214      215       +1     

Impacted Files	Coverage Δ
gptcache/manager/scalar_data/manager.py	90.47% <0.00%> (-4.77%)	⬇️
gptcache/processor/post.py	100.00% <ø> (ø)
gptcache/similarity_evaluation/distance.py	100.00% <ø> (ø)
gptcache/adapter/adapter.py	87.32% <100.00%> (ø)
gptcache/similarity_evaluation/onnx.py	95.83% <100.00%> (ø)
gptcache/utils/softmax.py	100.00% <100.00%> (ø)