Cannot load a list of commits for SHA256 commits

Problem

Commits page returns 404 because it doesn't support SHA256 commits.

Reproduction steps

1. Setup a SHA256 repository in GDK (for example import https://staging.gitlab.com/pks-gitlab/gitaly-sha256.git)
2. Click on latest commit
3. Go to commits page

Suggestion

Update SHA detection logic to support SHA256: https://gitlab.com/gitlab-org/gitlab/blob/3e10824cc3ed25e6ae5d206752af6acf756c2f98/lib/extracts_ref.rb#L123