utf-8 branch name issue in SymbolicReference._get_ref_info_helper

[grho]

Hi,
a branch is shown incorrectly when contains utf-8 characters

Branch name:
refs/heads/zażółć_gęślą_jaźń

The issue can be fixed by adding encoding in SymbolicReference._get_ref_info_helper.
Proposed change:
Replace

with open(osp.join(repodir, ref_path), 'rt') as fp:

Current result (e.g. shown as active_branch):
refs/heads/zażółć_gęślą_jaźń

with

with open(osp.join(repodir, ref_path), 'rt', encoding="utf-8") as fp:

Expected result:
refs/heads/zażółć_gęślą_jaźń

[Byron]

Thanks for letting me know! Unfortunately, GitPython is full of encoding issues, and even though assuming UTF-8 isn't technically a perfect fix, it's definitely an improvement over using ASCII implicitly.

I would be happy to receive a PR for that.

[Harmon758]

Duplicate of #774