[MacPorts] #56664: enable diff-highlight in git, with variant

[MacPorts]

#56664: enable diff-highlight in git, with variant
----------------------+----------------------
  Reporter:  iEFdev   |      Owner:  ci42
      Type:  request  |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:  2.5.2
Resolution:           |   Keywords:  haspatch
      Port:  git      |
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Changes (by iEFdev):

 * Attachment "Portfile_diff_highlight.diff" added.


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Ticket URL: <https://trac.macports.org/ticket/56664>
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