[MacPorts] #69345: Lean: Update to Lean 4

[MacPorts]

#69345: Lean: Update to Lean 4
----------------------+--------------------
 Reporter:  szhorvat  |      Owner:  (none)
     Type:  defect    |     Status:  new
 Priority:  Normal    |  Milestone:
Component:  ports     |    Version:
 Keywords:            |       Port:  lean
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 Please update the `lean` port to Lean 4, or alternatively provide Lean 4
 through a new port.

 The official Lean installation instructions suggest executing a shell
 script directly from GitHub, which then proceeds to install Homebrew, and
 thus doesn't play well with an existing MacPorts installation. Installing
 Lean would be much easier for MacPorts users if it were provided as a
 port.

 https://leanprover-community.github.io/install/macos.html

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Ticket URL: <https://trac.macports.org/ticket/69345>
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