Missing scrollbar in two dimensional filter

Issue Summary

In Jira (this occurred in 8.21.x), when you add a Two Dimensional Filter Statistics gadget, the dropdown list of the field "XAxis" and "YAxis" doesn't have a scrollbar to navigate between the option, so you'll be unable to select some options if you have several options to choose.

Steps to Reproduce

1. Add a Two Dimensional Filter Statistics gadget to a dashboard
2. Expand "XAxis"(or "YAxis") dropdown list.

Expected Results

If the list is greater than the screen, it should have a scrollbar.

• This screenshot is from Jira 8.19.1
  

Actual Results

If the list is greater than the screen, there is no scrollbar.

• On 8.21.1
  

Workaround

• You should still be able to select the option through the keyboard arrow, although you can't see the option where selecting.
• Field supports filtering, so you can remove current value of the field and start typing name of desired custom field. List of available options should be reduced to match typed phrase.