Fix linting

[Hypnosphi]

See CI failure for #1848:
https://circleci.com/gh/storybooks/storybook/12156?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

[codecov]

Codecov Report

Merging #1854 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1854   +/-   ##
=======================================
  Coverage   21.33%   21.33%           
=======================================
  Files         257      257           
  Lines        5737     5737           
  Branches      695      691    -4     
=======================================
  Hits         1224     1224           
+ Misses       3977     3975    -2     
- Partials      536      538    +2

Impacted Files	Coverage Δ
lib/ui/src/modules/ui/components/layout/usplit.js	38.7% <100%> (ø)	⬆️
lib/ui/src/modules/ui/containers/down_panel.js	23.52% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/left_panel/header.js	29.62% <0%> (ø)	⬆️
...res__/update-addon-info/update-addon-info.input.js	0% <0%> (ø)	⬆️
addons/storyshots/src/require_context.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/PropForm.js	8.51% <0%> (ø)	⬆️
app/react/src/client/preview/error_display.js	0% <0%> (ø)	⬆️
lib/ui/src/libs/key_events.js	23.25% <0%> (ø)	⬆️
addons/info/src/components/markdown/htags.js	30% <0%> (ø)	⬆️
lib/ui/src/modules/ui/libs/hierarchy.js	48.8% <0%> (ø)	⬆️
... and 18 more

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[ndelangen]

Was already fixed on release/3.3