Fix encoding error for commits endpoint

What does this MR do and why?

Contributes to #407848 (closed)

Problem

We started displaying tags on commits page. However, tags with UTF-8 characters raise an exception, because we don't encode them correctly.

Solution

Use 'Git#ref_name' to convert tag name to UTF-8 format.

How to set up and validate locally

1. Create tag with name tést in the repository
2. Go to page http://127.0.0.1:3000/root/encoding-error/-/commits/master
3. You should see the list of commits (without the fix - 500 error)

MR acceptance checklist

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