[MacPorts] #71972: qt5: Update to last stable 5.15.16.

[MacPorts]

#71972: qt5: Update to last stable 5.15.16.
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  Reporter:  cgilles  |      Owner:  MarcusCalhoun-Lopez
      Type:  update   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:
Resolution:           |   Keywords:
      Port:  qt5      |
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Comment (by reneeotten):

 when the newer version was released and I tried to update the port, it
 failed building somewhere and I haven't had the time/interest to
 troubleshoot that. Again, you should feel free to attempt the update
 yourself and submit a PR once everything works.

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Ticket URL: <https://trac.macports.org/ticket/71972#comment:3>
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