[MacPorts] #44804: Update protobuf-cpp to 2.6.0

[MacPorts]

#44804: Update protobuf-cpp to 2.6.0
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  Reporter:  nomis52@…     |      Owner:  blair@…
      Type:  update        |     Status:  new
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:
Resolution:                |   Keywords:
      Port:  protobuf-cpp  |
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Comment (by adfernandes@…):

 I've updated '''and tested''' `protobuf-cpp`, `protobuf-java`,
 `protobuf-c`, and `py-protobuf`.

 Unfortunately, python3 still isn't supported. Oh well.

 Patch is attached. I can merge, if that's okay with blair and landonf.

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Ticket URL: <https://trac.macports.org/ticket/44804#comment:2>
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