Filter autocomplete dropdowns get closed on scrollbar click

Summary

It is currently not possible to use the scrollbar in filter autocomplete dropdowns, as clicking on the scrollbar closes the dropdown.

Steps to reproduce

1. Go to an issue list page
2. Begin creating a filter (e.g. Label =) to open an autocomplete dropdown
3. Try to scroll using the scrollbar

What is the current bug behavior?

When clicking on the scrollbar (on mousedown), the whole autocomplete dropdown gets closed.

What is the expected correct behavior?

It should be possible to use the scrollbar without closing the dropdown.

Relevant logs and/or screenshots

bug

Results of GitLab environment info

GitLab 13.10 (gitlab.com) and GitLab 13.9.3, tested with Chrome and Firefox.