[MacPorts] #56975: livecheck broken in GitHub PortGroup

[MacPorts]

#56975: livecheck broken in GitHub PortGroup
--------------------+--------------------
 Reporter:  l2dy    |      Owner:  (none)
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:
 Keywords:          |       Port:
--------------------+--------------------
 GitHub is returning different content with and without `Accept: text/html`
 header.

 {{{
 $ port -v live h2o
 Error: cannot check if h2o was updated (regex didn't match)
 $ curl 'https://github.com/h2o/h2o/tags'
   <li role="option" class="autocomplete-item">v2.3.0-beta1</li>
   <li role="option" class="autocomplete-item">v2.2.5</li>
   <li role="option" class="autocomplete-item">v2.2.4</li>
   <li role="option" class="autocomplete-item">v2.2.3</li>
   <li role="option" class="autocomplete-item">v2.2.2</li>
   <li role="option" class="autocomplete-item">v2.2.1</li>
   <li role="option" class="autocomplete-item">v2.2.0</li>
   <li role="option" class="autocomplete-item">v2.2.0-beta3</li>
   <li role="option" class="autocomplete-item">v2.2.0-beta2</li>
 }}}

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Ticket URL: <https://trac.macports.org/ticket/56975>
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