[MacPorts] #65623: ffmpeg: update to 6.x

[MacPorts]

#65623: ffmpeg: update to 6.x
-------------------------+----------------------
  Reporter:  janngobble  |      Owner:  mascguy
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.7.2
Resolution:              |   Keywords:
      Port:  ffmpeg      |
-------------------------+----------------------

Comment (by badger200):

 @tobias : 6.1 breaks videotoolboxenc.c due to
 > libavcodec/videotoolboxenc.c:1185:40: error: use of undeclared
 identifier 'kVTCompressionPropertyKey_EncoderID';
 Which is 10.13 specific. I’m building on 10.9. 6.0 is built and installed
 currently.

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Ticket URL: <https://trac.macports.org/ticket/65623#comment:20>
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