Repository.resolve_refish does not return a commit if given annotated tag SHA

The repository.resolve_refish function is meant to return a commit object as the first element of the tuple ( source ).

However, if given a SHA of an annotated tag, it returns a tag object instead, which causes problems downstream.

The SHA of the target commit is available under result.target (see below)

How to reproduce:

Execute the following (clone the pygit2 repo into a temporary dir, create an annotated tag):

import pygit2
from pathlib import Path
import tempfile

repo_dir = tempfile.TemporaryDirectory()
repo_path = Path(repo_dir.name)

repo = pygit2.clone_repository("https://github.com/libgit2/pygit2.git", repo_path)
head_sha = repo.head.peel().id

old = repo.create_tag(
    'test_annotated_tag',
    head_sha,
    pygit2.GIT_OBJ_COMMIT,
    pygit2.Signature('John Doe', 'jdoe@example.com', 12347, 0),
    'message'
)

commit, ref = repo.resolve_refish(str(old))

Then we can investigate the results:

In [2]: commit  # not really a commit!
Out[2]: <pygit2.Object{tag:66986bf4eb1e47c3049f5a146609f0aa7b64757d}>

In [3]: commit.target
Out[3]: e2c0fdbfbd7f84374f8c7a3df256547b7ea99192

In [4]: head_sha
Out[4]: e2c0fdbfbd7f84374f8c7a3df256547b7ea99192

Start in pygit2/repository.py at the resolve_refish implementation referenced in the issue. Reproduce the annotated-tag SHA case with the provided script, then trace the returned object and its target. Done means the first tuple element is a commit object for this case and the existing behavior remains intact for other refish inputs.