Merge request description field does not allow scrolling independently from page

Summary

The merge request description field does not allow independent scrolling when in "edit" mode. Only the page scrolls not the description field.

If I type any character on the description field, the ability to scroll independently comes back ¯_(ツ)_/¯

Steps to reproduce

Click "edit" on any MR, attempt to scroll the description field.

What is the current bug behavior?

Description field does not allow independent scrolling from page

What is the expected correct behavior?

Description field allows independent scrolling from page

Relevant logs and/or screenshots

Output of checks

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Results of GitLab environment info

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Results of GitLab application Check

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sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

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