Web: Can't scroll edit post textbox

Description

Environment: Chrome/Mac and Firefox/Mac on community-release and master

Repro steps:
1) Send a post that's long enough to cause the edit post box to scroll
2) Edit the post
3) Try to scroll using the scroll wheel, track pad, or clicking on the scroll bar

Observed: You aren't able to scroll the textbox. If you click on another window and then back onto Mattermost, you might be able to scroll again
Expected: You can scroll as soon as the window opens

QA Test Steps

See description

Status

Mana

None

Assignee

Asaad Mahmood

QA Assignee

Jelena Gilliam

Reporter

Harrison Healey

Epic Link

None

Fix versions

Mattermost Team

UX

Sprint

None

Labels

None

QA Testing Areas

Other (write in QA test steps)

GitHub Issue

None

Components

None
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