[MacPorts] #63529: opencolorio: fix compatibility with yaml-cpp-0.7.0

[MacPorts]

#63529: opencolorio: fix compatibility with yaml-cpp-0.7.0
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  Reporter:  devernay     |      Owner:  (none)
      Type:  defect       |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:  2.7.1
Resolution:               |   Keywords:
      Port:  opencolorio  |
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Comment (by cooljeanius):

 Note that this breaks rev-upgrade of opencolorio, and blocks installation
 of blender, as per #62891

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Ticket URL: <https://trac.macports.org/ticket/63529#comment:2>
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