[MacPorts] #59538: github portgroup doesn't work with default master_sites from other portgroups

[MacPorts]

#59538: github portgroup doesn't work with default master_sites from other
portgroups
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  Reporter:  jmroot  |      Owner:  (none)
      Type:  defect  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:
      Port:          |
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Comment (by ryandesign):

 I can commit it tonight, if nobody else beats me to it. But if you do
 commit it, please monitor the buildbot for failures and see if they might
 be because of this change.

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Ticket URL: <https://trac.macports.org/ticket/59538#comment:9>
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