[MacPorts] #63974: GitHub CI: update PR workflow to cancel outdated jobs on push

[MacPorts]

#63974: GitHub CI: update PR workflow to cancel outdated jobs on push
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  Reporter:  mascguy         |      Owner:  admin@…
      Type:  enhancement     |     Status:  new
  Priority:  Normal          |  Milestone:
 Component:  server/hosting  |    Version:  2.7.1
Resolution:                  |   Keywords:  github ci
      Port:                  |
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Changes (by mascguy):

 * cc: neverpanic (added)


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Ticket URL: <https://trac.macports.org/ticket/63974#comment:1>
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