Add new diff note icon on commit page is currently broken on Canary

Summary

Add diff note icon is currently displayed without proper styles.

Steps to reproduce

It's broken on any project on Canary and here is one example 890fe7e3

Example Project

Any projects on Canary

What is the current bug behavior?

Incorrectly styled note icon

What is the expected correct behavior?

Corectly styled note icon like this

Relevant logs and/or screenshots

Output of checks

Canary on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
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

It seems to have been introduced by this !35371 (merged) and the fix would be reverting some of the change for Commit Show page which may have been overlooked.