[MacPorts] #57923: carthage @0.30.1_0: update to 0.31.2

[MacPorts]

#57923: carthage @0.30.1_0: update to 0.31.2
-------------------------+------------------------
  Reporter:  FranklinYu  |      Owner:  seanfarley
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  carthage    |
-------------------------+------------------------

Comment (by FranklinYu):

 In addition, the
 [https://github.com/Carthage/Carthage/tree/master/Source/Scripts Bash/Zsh
 completion] was not installed with the package. Refer to
 [https://github.com/Homebrew/homebrew-
 core/blob/d7df4375a5fcba6f8d269df8e7b04184ffaf3b85/Formula/carthage.rb#L20-L22
 installation in Homebrew].

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Ticket URL: <https://trac.macports.org/ticket/57923#comment:1>
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