devel/ruby-git: update to 1.18.0

1.18.0 (2023-03-19)

Changes since v1.17.2:

* 3c70 Add support for --update-head-ok to fetch (#660)
* b53d Do not generate yard documentation when building in TruffleRuby
  (#659)
* 5af1 Correctly report command output when there is an error (#658)
* b27a Add test to ensure that Git.open works to open a submodule (#655)
* 5b0e Update Git.clone to set multiple config variables (#653)

(taca)