[MacPorts] #60876: Upgrade GIMP2 port to GIMP 2.10.20

[MacPorts]

#60876: Upgrade GIMP2 port to GIMP 2.10.20
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 Reporter:  jacbou  |      Owner:  dbevans
     Type:  update  |     Status:  assigned
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:
 Keywords:  update  |       Port:  gimp2
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 The GIMP team has released GIMP 2.10.20 a couple of weeks ago. Would be
 great to update the port to the latest version as also the GIMP team
 itself does not provide a Mac port to download.

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Ticket URL: <https://trac.macports.org/ticket/60876>
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