[MacPorts] #40076: libgit2: update to 0.19.0

[MacPorts]

#40076: libgit2: update to 0.19.0
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  Reporter:  nvenegas@…  |      Owner:  macports-tickets@…
      Type:  update      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:  haspatch
      Port:  libgit2     |
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Comment (by nvenegas@…):

 With "archive" it fetched from
 "https://github.com/libgit2/libgit2/tarball/v0.19.0".

 With "tags" it also fetched from
 "https://github.com/libgit2/libgit2/tarball/v0.19.0".

 I guess I hit the fall through logic with "archive". I'll update the
 attached patch.

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Ticket URL: <https://trac.macports.org/ticket/40076#comment:5>
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