[MacPorts] #70291: Add portimage_mode to macports.conf on APFS builders

[MacPorts]

#70291: Add portimage_mode to macports.conf on APFS builders
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  Reporter:  jmroot         |      Owner:  admin@…
      Type:  enhancement    |     Status:  new
  Priority:  Normal         |  Milestone:
 Component:  buildbot/mpbb  |    Version:
Resolution:                 |   Keywords:
      Port:                 |
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Comment (by ryandesign):

 If you want me to make a change on the build machines, please tell me
 exactly what you want changed. I don't know what this is about or what the
 implications of the change are. One of the main concerns on the build
 machines is available disk space, so if your proposal frees up disk space
 that would be good, and if it takes up more disk space then that will
 cause more ports to fail to build due to lack of disk space. The x86_64
 macOS 13 and 14 build machines have ample free space so one of them could
 be used for an initial test.

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Ticket URL: <https://trac.macports.org/ticket/70291#comment:1>
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