By default, Git allows the pathspec to have glob patterns
(https://css-tricks.com/git-pathspecs-and-how-to-use-them), but the
LastCommitForPath RPC now supports a `literal_pathspec` to disable this
(https://gitlab.com/gitlab-org/gitaly/-/merge_requests/2285). We now use
this whenever we look up specific files in the repository.

Closes https://gitlab.com/gitlab-org/gitaly/-/issues/2857