use concurrency for cancelling previous ci jobs

[nihui]

No description provided.

[codecov-commenter]

Codecov Report

Merging #3405 (b32a915) into master (426e564) will increase coverage by 0.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3405      +/-   ##
==========================================
+ Coverage   90.79%   91.03%   +0.23%     
==========================================
  Files         527      481      -46     
  Lines      144319   116532   -27787     
==========================================
- Hits       131034   106084   -24950     
+ Misses      13285    10448    -2837     

Impacted Files	Coverage Δ
src/layer/crop.cpp	86.45% <0.00%> (-3.21%)	⬇️
src/layer/x86/relu_x86.cpp	74.73% <0.00%> (-3.05%)	⬇️
src/allocator.cpp	73.98% <0.00%> (-3.02%)	⬇️
src/layer/x86/convolution_3x3.h	23.94% <0.00%> (-2.77%)	⬇️
src/layer/x86/reshape_x86.cpp	91.94% <0.00%> (-2.56%)	⬇️
src/layer/riscv/deconvolution_packnto1.h	97.95% <0.00%> (-2.05%)	⬇️
src/layer/x86/flatten_x86.cpp	94.81% <0.00%> (-1.75%)	⬇️
src/layer/x86/cast_x86.cpp	96.05% <0.00%> (-1.68%)	⬇️
src/layer/x86/pooling_x86.cpp	94.11% <0.00%> (-1.48%)	⬇️
src/layer/x86/binaryop_x86.cpp	94.75% <0.00%> (-0.96%)	⬇️
... and 100 more

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