Fix directory and last commit not loading for special filenames

Filenames that contained special pathspec characters (see
https://css-tricks.com/git-pathspecs-and-how-to-use-them) would not
return a valid last commit or properly load in the repository
browser. For example, `:wq` would cause the GraphQL endpoint to return a
null `lastCommit`, and a file `:wq/test.txt` would not show the commit
information in the repository browser.

This requires https://gitlab.com/gitlab-org/gitaly/-/merge_requests/2303
to work.