Set version 3.8.0

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[codecov]

Codecov Report

Attention: Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.

Project coverage is 66.65%. Comparing base (e93c0d3) to head (cf0ab00).
Report is 28 commits behind head on develop.

Files with missing lines	Patch %	Lines
test/conductivity/test_kappa_LBTE.py	77.77%	4 Missing ⚠️
phono3py/conductivity/utils.py	33.33%	2 Missing ⚠️
phono3py/phonon/solver.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #303      +/-   ##
===========================================
+ Coverage    66.45%   66.65%   +0.19%     
===========================================
  Files           73       73              
  Lines        12852    12901      +49     
===========================================
+ Hits          8541     8599      +58     
+ Misses        4311     4302       -9     

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