feat: accept the fullname of branch

[LinuxSuRen]

The branch name could be master or refs/heads/master.

[codecov]

Codecov Report

Merging #14 (7ada3ce) into master (8052720) will increase coverage by 1.63%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   40.63%   42.27%   +1.63%     
==========================================
  Files           5        5              
  Lines         219      220       +1     
==========================================
+ Hits           89       93       +4     
+ Misses        130      127       -3     

Flag	Coverage Δ
unittests	42.27% <100.00%> (+1.63%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/checkout.go	37.11% <100.00%> (+3.78%)	⬆️

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