Labels dropdown wrong height

Summary

The height for the "Labels" dropdown when creating a merge request is too tall for its container

Steps to reproduce

1. Start creating a new merge request
2. Click the dropdown to add a label
3. Notice that the height isn't tall enough and it overflows

What is the current bug behavior?

The container overflows

What is the expected correct behavior?

The container should have enough space to not overflow

Relevant logs and/or screenshots

Possible fixes

I set the div with class "dropdown-menu dropdown-select dropdown-menu-paging dropdown-menu-labels dropdown-menu-selectable" max-height to 323px

Using flexbox is a way better solution