[MacPorts] #56369: github portgroup: don't override an already-specified version

[MacPorts]

#56369: github portgroup: don't override an already-specified version
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  Reporter:  ryandesign  |      Owner:  (none)
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:              |
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Comment (by ryandesign):

 The longer-term project is to remove the `github.setup` procedure
 entirely, because we now consider `.setup` procedures to be an
 antipattern. Once we do that, the problem goes away. But I haven't given
 sufficient thought to that project yet to be able to implement it.

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Ticket URL: <https://trac.macports.org/ticket/56369#comment:1>
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