[MacPorts] #43216: gtk3: update to version 3.12.0

[MacPorts]

#43216: gtk3: update to version 3.12.0
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  Reporter:  devans@…  |      Owner:  cal@…
      Type:  update    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.2.1
Resolution:            |   Keywords:
      Port:  gtk3      |
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Changes (by devans@…):

 * type:  defect => update


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Ticket URL: <https://trac.macports.org/ticket/43216#comment:1>
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