chore(deps): update dependency @gitlab/ui to v21.4.0

This MR contains the following updates:

Package	Type	Update	Change
@gitlab/ui (source)	dependencies	minor	21.3.0 -> 21.4.0

MR created with the help of gitlab-org/frontend/renovate-gitlab-bot

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Release Notes

gitlab-org/gitlab-ui

v21.4.0

Compare Source

Features

• GlButton: Add button-text-class prop to gl-button (2caaa3b)

21.3.1 (2020-09-16)

Bug Fixes

• GlChart: Tooltip title values not displaying (dea6750)

v21.3.1

Compare Source

Bug Fixes

• GlChart: Tooltip title values not displaying (dea6750)

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