Issues search for queries containing non-ascii characters

Summary

Issue search doesn't return results if query contains non-ascii characters.

Steps to reproduce

1. Create an issue with title containing both ascii and non-ascii words.
2. Go to issue list.
3. Search for a word containing only ascii characters, it works.
4. Search for a word containing both ascii and non-ascii characters, it doesn't return results.

Example Project

Issues

1. https://gitlab.com/Oscik/test-gitlab-search/-/issues/1
2. https://gitlab.com/Oscik/test-gitlab-search/-/issues/2

Search results

1. https://gitlab.com/Oscik/test-gitlab-search/-/issues/?search=k%C3%B6ln
2. https://gitlab.com/Oscik/test-gitlab-search/-/issues/?search=berlin
3. https://gitlab.com/Oscik/test-gitlab-search/-/issues/?search=pozna%C5%84
4. https://gitlab.com/Oscik/test-gitlab-search/-/issues/?search=warszawa

What is the current bug behavior?

No results are returned for queries containing non-ascii keywords.

What is the expected correct behavior?

There should be results both for ascii and for non-ascii keywords.

Output of checks

This bug happens on GitLab.com.