Return an error for an invalid ref_name

What does this MR do and why?

• Contributes to #351520 (closed)
• Sentry error: https://sentry.gitlab.net/gitlab/gitlabcom/issues/3173142/

Problem

Git ref cannot start with -. Currently we return an ArgumentError from the Gitaly.

Solution

Verify the ref_name with regexp

Screenshots or screen recordings

How to set up and validate locally

http://127.0.0.1:3000/api/v4/projects/6/repository/commits?ref_name=-main

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.