Log Message:
devel/libgit2: update to 1.2.0

libgit2 1.3.0 is already released, but I'm not sure ruby-rugged 1.2.0
support it.

1.2.0 (2021-09-02)

Changes are too many to write here, please refer
<https://github.com/libgit2/libgit2/releases/tag/v1.2.0>.