[EuiComboBox] Fixed options list misalignment

[wenchonglee]

Summary

Fixes #4472.

@chandlerprall explained how to reproduce the problem and why it is happening
#4472 (comment)

To test it on the docs page, use devtools to manually remove enough elements so that only 1 EuiComboBox is left, then mimic the clip shared in the issue.

Checklist

• Check against all themes for compatibility in both light and dark modes
• Checked in mobile
• Checked in Chrome, Safari, Edge, and Firefox
  - [ ] Props have proper autodocs and playground toggles
  - [ ] Added documentation
  - [ ] Checked Code Sandbox works for the any docs examples
  - [ ] Added or updated jest tests
• Checked for breaking changes and labeled appropriately
  - [ ] Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[thompsongl]

jenkins test this

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4607/

[thompsongl]

jenkins test this

Somewhat confused about the cause of this snapshot failure:

-  style="top: 16px; left: -22px; z-index: 2000; will-change: transform, opacity;"
+  style="top: 16px; left: -22px; will-change: transform, opacity; z-index: 2000;"

[cchaos]

This isn't up to date with master. That change came from #4590

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4607/

[wenchonglee]

Hmm, that was weird, I thought I was up to date at the time of submitting this PR. Please try again, I've tried running the test locally this time.

[thompsongl]

jenkins test this

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4607/

[thompsongl]

Running CI again to be safe

jenkins test this

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4607/

[thompsongl]

Thanks, @wenchonglee!