Some dropdowns have two scroll bars.

Summary

Some dropdowns have two scroll bars.

Steps to reproduce

One example:

1. Visit any MR with more than ~5 changed files, e.g. !17081 (merged)
2. Go to the "Changes" tab
3. Open the "Changed files" dropdown
4. Scroll down in the dialog until the second scrollbar appears (depending on your OS you may see it right when you open the dialog, on macOS it depends on your system settings)

Another example:

1. Visit the project files page
2. Open the branches/tags dropdown
3. Scroll down in the dialog until the second scrollbar appears (depending on your OS you may see it right when you open the dialog, on macOS it depends on your system settings)

What is the current bug behavior?

There are two scrollbars.

What is the expected correct behavior?

There should only be one scrollbar.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com. I'm pretty sure it was introduced by the 10.5.0 release candidates.

Possible fixes

I assume this commit might be related?: 0d85e1b4

It looks like we enabled overflow on the dropdown container, which is causing the second scroll bar. At least that's my assumption.

Also reported by #43249 (closed)