[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 reneeotten):

 this change solves the issue I was seeing yesterday when using both the
 github and python PG; but I cannot reaaly tell if there are unintended
 side-effects from this change. If not, I'd vote for making this change.

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Ticket URL: <https://trac.macports.org/ticket/59538#comment:8>
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