Mentions dropdown in PR description box is clipped

Issue Summary

On Edit dialog in PR page, the dropdown for user mentions is not completely shown and is clipped within the Edit dialog

Steps to Reproduce

1. Create a PR or Go to an existing page
2. Click Edit, an Edit dialog opens up
3. Start typing `@` to mention a user somewhere near the bottom of the description box

Expected Results

Mentions dropdown values should be shown fully even if it overflows

Actual Results

Mentions dropdown is clipped

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available