[MacPorts] #69722: openimageio: Add and default to python312 variant

[MacPorts]

#69722: openimageio: Add and default to python312 variant
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 Reporter:  ryandesign   |      Owner:  MarcusCalhoun-Lopez
     Type:  enhancement  |     Status:  assigned
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:               |       Port:  openimageio
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Ticket URL: <https://trac.macports.org/ticket/69722>
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