git: pass `id` attribute of `pygit2.Tree` object `pygit2`'s Repository object expects an instance of `Oid` to return the corresponding object, instead of the object itself. After this change and D9062, `hg commit -i` seems to work, unless it hits a case folding assertion (ie trying to add a file like `README.md`). Differential Revision: https://phab.mercurial-scm.org/D9068